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DRLRM1.WS4 (= "Dr. Logo Reference Manual", Section 1) ---------- (Retyped by Emmanuel ROCHE. Posted to comp.os.cpm.amethyst by Roche on 18 Apr 2005.) Section 1: Components of Dr. Logo --------------------------------- A procedure is an action that Dr. Logo can do. A Logo program is made up of procedures. You will probably start by writing one- procedure programs, but you will build your first procedures out of procedures that come with Dr. Logo, called "Dr. Logo primitives". Later, you will use the procedures that you have written, as well as Dr. Logo primitives, to build complex programs. Procedures are the basic building blocks for programming with Dr. Logo. A procedure is made up of expressions. An expression has two parts: a procedure name and inputs to the procedure. That is why you need Dr. Logo primitives to build your first procedure. To Dr. Logo, everything you type is either a procedure name or an input to a procedure. Although you can build a procedure out of many expressions, you can also ask Dr. Logo to evaluate expressions one at a time by entering them individually to the ? prompt, which is sometimes called the interpreter or toplevel. For example, ?print "Salutations! Salutations! In this example, print "Salutations! is an expression. The procedure name "print" identifies a Logo primitive that displays its input, Salutations!, on the screen. As in all examples in this book, the line following "?" shows what the user types at the keyboard. After you type a line at toplevel, you must press the Enter key, <--+, to tell Dr. Logo that you want the expressions on the line evaluated. A procedure can require a certain number and kind of inputs. Input to a procedure can be words, numbers, or lists. This section formally defines how to put characters together to form procedure names, words, numbers, and lists, so that you can combine them into expressions. Then, it tells you how Dr. Logo evaluates a line when you put more than one expression on it. 1.1 Dr. Logo character set -------------------------- To build a procedure name or word, you can use almost any character on your keyboard, including upper- and lowercase letters, numerals, and symbols. For example box1 box2 RobinNest draw&go However, Logo gives special meaning to certain characters. For example, blank spaces delimit words or numbers; a blank space before and a blank space after a word set the word off from the rest of the line. The following special characters are also Logo delimiters: Table 1-1. Dr. Logo special characters Character Type Action/use --------- ---------- ---------- [ Begins a list ] Ends a list ( Begins a grouped expression ) Ends a grouped expression ; Begins comments = logical Equal infix operation, outputs TRUE or FALSE < logical Less-than infix operation, outputs TRUE or FALSE > logical Greater-than infix operation, outputs TRUE or FALSE + arithmetic Addition prefix operation, outputs sum of inputs. - arithmetic Subtraction infix operation, outputs difference of two inputs. * arithmetic Multiplication infix operation, outputs product of inputs. / arithmetic Division infix operation, outputs quotient of inputs. ^ arithmetic Exponent infix operation, outputs first input number raised to the second input power. When you use a delimiter in an expression, you do not need to precede it with a blank to set it off from the rest of the line. Whenever one of these characters appears, Dr. Logo assumes that it starts a new word or number separate from anything else on the line. This simplifies typing expressions in many cases, such as 256+1026 but complicates using these characters in situations other than those that Dr. Logo expects. For example, if you try to use a dash as a hyphen (instead of a minus sign), you might see Dr. Logo add unwanted spaces: ?print [high-resolution turtle graphics] high - resolution turtle graphics To tell Logo that you want it to treat a delimiter as a part of a word, precede the special character with a backslash ("\") called "the quoting character" by Dr. Logo, which generates it when you type Ctrl-Q. ?print [high\-resolution turtle graphics] high-resolution turtle graphics Dr. Logo recognizes other special characters called "control characters" as commands. Control characters can edit a procedure, interrupt and terminate a procedure, and change between full text, full graphics, and splitscreens. Section 3, "Editing Commands", and Section 4, "Text and Graphic Screens", describe Dr. Logo control characters. 1.2 Logo objects ---------------- A Logo procedure can require a specific number and kind of inputs to perform its task. The required input can be one or more words, lists, or numbers. When a procedure requires any one of these, we say that it can accept a "Logo object", meaning that it needs a word, a list, or a number to complete its operation. To make your procedures more flexible, you can represent objects with names called "variables". This section describes words, lists, numbers, and variables. 1.2.1 Words ----------- A Logo word is a group of one or more consecutive characters separated from other characters on the line by delimiters. A blank space separates a word from the rest of the characters that follow it on the line. You can use periods (".") or underbars ("_") as connectors to make Dr. Logo treat several words as one word, as in the following example: ?print "choc.chip choc.chip ?print "oatmeal_raisin oatmeal_raisin In English, a sentence is composed of words called "verbs" and "nouns". In Logo, an expression is composed of words called "procedure names" and "inputs", which can be other names. Dr. Logo needs a way to distinguish an input name (noun) from a procedure name (verb). So, when you type a Logo expression, you must precede an input name with quotes ("). If you do not, Logo complains. For example, ?print "hi_there hi_there ?print hi_there I don't know how to hi_there Although quotes have this special meaning at the beginning of a word, they are not a delimiter, and can be use as a normal character within a word. Do not use quotes at the beginning of a word, except for this reason. Dr. Logo has a special primitive, quote, that has the same effect as quotes. ?print quote hi_there hi_there Other Dr. Logo primitives can examine a word character by character, take a word apart, and put a word together. When manipulating a word in one of these ways, Logo treats a character in a word as a one-letter word. For example, ?first "zebra z ?first first "zebra z ?first "z z ?butfirst "atypical typical ?last "rough h ?butlast "dates date ?word "R2 "D2 R2D2 As mentioned in Section 1.1, "Dr. Logo character set", you can tell Dr. Logo that you want to use a delimiter character in a word by preceding the delimiter with a backslash ("\"). However, if a delimiter character is the first character in the word, and the word is preceded by quotes ("), in most cases you do not have to put a backslash between the quotes and the delimiter character. ?"+more +more ?ascii "* 43 However, blank spaces and square brackets ("[" and "]") are treated as delimiters, even when preceded by quotes ("). Use a backslash ("\") after quotes (") to tell Logo to treat a space or square brackets as a normal character. ?ascii "[ ascii doesn't like an empty word as input ?ascii "\[ 93 The Dr. Logo primitive "readquote" (or "rq") creates a word that contains all the characters in a line typed at the keyboard. If the line contains delimiters, readquote inserts backslant characters in front of each one, to make the line one word. You can use readquote to create a command line for a function key to recall; fkey requires a word as input. See the following example. ?fkey 2 rq setd "b: resetd ?setd "b: resetd <Ctrl-G> <Enter> 1.2.2 Lists ----------- A literal list is a series of Logo objects enclosed in square brackets ("[" and "]"). You can create a list without square brackets by using the "list" or "sentence" primitive. Each element of a list can be a word, a number, or another list. Within the list, objects are delimited from one another by spaces. Dr. Logo treats every object in a literal list as a literal object, so you do not need to put quotes in front of a word included within a literal list. The following are valid literal lists: [Salutations!] [L M N] [[bread butter] [soup sandwich] [cheese crackers]] [10 20 [22 25] 30] The following examples show how to create a list using "sentence" and "list": ?list "L "M "N [L M N] ?sentence [I like] "hamburgers [I like hamburgers] The same Logo primitives that manipulate elements of words manipulate elements of lists. ?butfirst [not really] [really] ?butlast [not really] [not] ?fput 5 [10 20 [22 25] 30] [5 10 20 [22 25] 30] After the fput expression is executed, the list above has five elements, the fourth of which is a list. The following example shows how to count elements of lists within lists: ?count [5 10 20 [22 25] 30] 5 ?count item 4 [5 10 20 [22 25] 30] 2 The following table compares the four primitives that can take two objects as input and output a word or list. Table 1-2. Comparison of list primitives Primitive Input 1 Input 2 Output --------- ------- ------- ------ list "yellow "green [yellow green] sentence "yellow "green [yellow green] fput "yellow "green "yellowgreen lput "yellow "green "greenyellow list "sky [is blue] [sky [is blue]] sentence "sky [is blue] [sky is blue] fput "sky [is blue] [sky is blue] lput "sky [is blue] [is blue sky] list [say hello] [to me] [[say hello] [to me]] sentence [say hello] [to me] [say hello to me] fput [say hello] [to me] [[say hello] to me] lput [say hello] [to me] [to me [say hello]] list [hello] [] [[hello] []] sentence [hello] [] [hello] fput [hello] [] [[hello]] lput [hello] [] [[hello]] 1.2.3 Numbers ------------- A number is one or more numerals separated from other characters on the line by spaces or other delimiters. A number is a kind of word, but you do not have to put quotes (") in front of a number, unless you want to use it as a variable name. Dr. Logo does not try to treat a word that starts with a numeral as a procedure name. In fact, Dr. Logo will not let you define a procedure name that starts with a numeral. A number can contain a + or - to indicate sign. But, because these special characters are delimiters and arithmetic operators as well as signs, you might accidentally combine two numbers into one expression. To prevent this, Dr. Logo interprets spaces and numbers combined with arithmetic operators as follows: 5-2 is interpreted as 3. 5 - 2 is also interpreted as 3. However, 5 -2 is interpreted as two numbers: 5 and -2. Dr. Logo uses two kinds of numbers: integers and decimal numbers. You can input negative or positive decimal numbers with up to 15 significant digits, and any integer between 2147483647 and -2147483648. Most arithmetic operations can accept either an integer or a decimal number as input. Some take integers as input, but output a decimal number. ?13 / 7 1.85714285714286 Dr. Logo supports primitives that convert decimal numbers to integers, create exponential and random numbers, and perform trigonometric and logarithmic functions. Internally, Dr. Logo uses both single- and double-precision integers and floating- point numbers. Dr. Logo always uses double-precision for calculations, but converts numbers to single-precision for display or storage when accuracy to 15 places is not compromised. Internally, numbers are stored in IEEE standard 64- bit format, in the dynamic range 10 to the power of -308 to 10 to the power of +308. In the world of mathematics, there are numbers that cannot be represented by numerals. Dr. Logo outputs special words that represent these numbers: +INF represents the positive infinite number, -INF represents the negative infinite number, and NAN represents "not a number" for any mysterious entity that is not a number at all. ?1/0 +INF ?-1/0 -INF ?0/0 NAN 1.2.4 Variables --------------- A variable is a "container" that holds a Logo object. A container in your kitchen labeled "Cookie Jar" might contain chocolate chip, peanut butter, some other kind of cookies, or no cookies at all. In Dr. Logo, a variable can have any name you give it, and contain any object -- word, number, or list. Here is the simplest way to create a variable: ?make "favorites [choc.chip peanut.but ! oatmeal.raisin cream.fill brownie pinwh! eel shortbread snickerdoodle] After the make expression is executed, the long list of cookie types has a name: "favorites. Referring to an object by a variable name lets you write an expression that is independent of the object it manipulates. For example, the person responsible for keeping the cookie jar filled could enter: ?if emptyp :cookie.jar [make "cookie.ja! r first shuffle :favorites] which means, if the cookie jar is empty, put the first kind of cookie from the shuffled list of favorites into the cookie jar. Because Logo programmers use variables frequently, they use several terms to describe the relationship between a variable's name and its contents. For example, if the make expression puts snickerdoodle in cookie.jar, a Logo programmer might describe the relationship in any or all of these ways: - cookie.jar is a variable, snickerdoodle is its value - cookie.jar is the name of snickerdoodle - cookie.jar contains snickerdoodle - cookie.jar is bound to snickerdoodle - snickerdoodle is the "thing" of cookie.jar - snickerdoodle is the contents of cookie.jar - snickerdoodle is the value of cookie.jar There are two ways to reference the contents of a variable: ?thing "cookie.jar snickerdoodle ?:cookie.jar snickerdoodle A colon (":") before a variable name makes Dr. Logo reference the contents of the variable, instead of treating the variable name as a word. No matter how you think of variables, remember that you can use a variable in an expression without being concerned about the variable's actual value. Variables help you write expressions that are independent of the data they manipulate. Section 2, "Working with Procedures", tells how to use variables within procedures. 1.3 Lines and expressions ------------------------- You can put as many expressions on a line as you wish, but a line at toplevel cannot contain more than 132 characters. In general, Dr. Logo evaluates expressions on a line from left to right. It treats everything, including other expressions, to the right of a primitive name or identifier as input to that primitive if the primitive requires an input. ?random 10 > 5 random doesn't like TRUE as input ?5 > random 10 FALSE However, Dr. Logo does not evaluate arithmetic expressions in strict left-to-right order. It evaluates / and * expressions first, from left to right, then goes back and evaluates + or - expressions. ?2 * 3 + 7 / 5 7.4 To make Dr. Logo evaluate expressions in a different order, you can group expressions in parentheses ["(" and ")"]. Dr. Logo evaluates the expression in the innermost parentheses first. The order in which Dr. Logo evaluates your expression can make a big difference in the output! ?(random 10) > 5 FALSE ?2*(3+7)/5 4 EOF DRLRM2.WS4 (= "Dr. Logo Reference Manual", Section 2) ---------- (Retyped by Emmanuel ROCHE.) Section 2: Working with procedures ---------------------------------- This section discusses several aspects of working with Dr. Logo procedures. It tells how to construct a procedure and give it multiple inputs. It also describes how Dr. Logo keeps track of executing procedures. 2.1 Constructing procedures --------------------------- The following sections describe how to put a procedure together: how to define it, how to make it readable, and how to use a variable to pass information between procedures and make a procedure require an input. 2.1.1 Naming and defining procedures ------------------------------------ To define a procedure is to teach Dr. Logo a new verb, that is to say, to tell Dr. Logo how to do a new thing. You teach Dr. Logo a new verb by describing the new activity with primitives and other words Dr. Logo already know or will know before you execute the procedure. For example, Dr. Logo knows primitives that make the turtle go forward, repeat, and turn right. Using these primitives, you can describe how to draw a square, and use that description to define a new procedure. The simplest way to define a new procedure is to begin a line with the special word "to", which makes Dr. Logo remember the next word you type as a new procedure name. Your procedure name should tell what your procedure does, and can start with any character, except a numeral. Dr. Logo will complain if you try to use the name of a primitive as a procedure name, unless you have set the system variable REDEFP to TRUE. When you start a line with "to", Dr. Logo gives you a new prompt character, >, to tell you it will not immediately execute the instructions that you enter to define the new procedure. ?to square >repeat 4 [forward 60 right 90] >end square defined ? The special word "end" tells Dr. Logo that you have finished defining your procedure, and returns you to the ? prompt. You must enter "end" by itself as the last line of a procedure. Now that "square" is defined, you can use square as a procedure name, as follows. Also see Colorplate 23 at the beginning of Section 6, "References to Primitives". ?square Logo programmers use terms similar to those they use for variables to describe the relationship of a procedure and its definition. Here is how these terms apply to the procedure just defined: - "to square" is the title line of square - square is the name of [repeat 4 [forward 60 right 90]] - [repeat 4 [forward 60 right 90]] is the definition of square - [repeat 4 [forward 60 right 90]] is the body of square The body of a procedure is a special kind of list: a list of expressions. This list can contain as many expressions as you want, or it can be an empty list. Because Dr. Logo treats the definition of a procedure as a list, you can write a procedure that first combines expressions into a list, and then defines this list as the body of a new procedure. The description of the "define" primitive in Section 6, "References to Primitives", tells how one procedure can define another. You can use the Dr. Logo screen editor to modify your procedures' definitions. When you use the editor, you can change the body of a procedure, add a new procedure, or change the title line of an existing procedure. When you exit the editor, the new or changed procedures are defined, replacing any previous definitions for those names. The descriptions of the ed, edall, and edps primitives in Section 6 tells how to load procedures into the Dr. Logo editor. Section 3, "Editing Commands", tells how to use the editor. 2.1.2 Writing readable procedures --------------------------------- All programmers want to make their procedures as readable as possible. A readable procedure is a distinct advantage when you try to share your work with friends, or try to use a procedure several months after writing it. Two traditional tools that make a program readable are short procedures and long names for procedures and variables. In general, short procedures are more readable than long ones. Short procedures are easier to understand, test, and combine with other procedures. Long procedure and variable names can help describe the purpose and function of procedures, or the kind of data represented by variables. However, long names take up valuable memory space, so you might have to shorten your names if you write a large program that needs all your workspace. Dr. Logo gives you special help in writing readable procedures. For example, Dr. Logo lets you break long expressions into two or more lines. Generally, a line in a procedure is a single expression: a procedure name and its inputs. However, some procedures need complex inputs, such as lists of instructions or predicate expressions. This kind of line can grow so long that it becomes difficult to read. For example, an "if" command with a long predicate expression and two instructions lists can easily exceed the width of your display. When this happens, Dr. Logo prints an exclamation point ("!") and displays the remainder of the command on the next line. ?to check.for.favorites >if memberp :cookie.jar :favorites (pr ! [edible cookies available] (pr [forget ! it!]) >end check.for.favorites defined You can clean up your procedure's appearance by breaking the long expression into several lines. If you press the Enter key and begin the next line with a space or a tab, Dr. Logo treats the new line as a continuation of the expression on the previous line. ?to check.for.favorites >if memberp :cookie.jar :favorites [pr [edible cookies available]] [pr [forget it!]] >end check.for.favorites defined Dr. Logo also lets you put comments in your procedures. A comment is text that Dr. Logo ignores and does not try to evaluate or execute. You can use comments to describe the function or purpose of a procedure or expression. You can start a comment at the beginning of a line or after the last expression on the line, but a comment must be the last object on the line. Start a comment with a semicolon (";"), as shown in the following example. Also see Colorplate 3. ?to triangle ; Draw an equilateral tri! angle >repeat 3 [forward 20 right 120] >end triangle defined ?to flag >fd 40 >triangle >back 40 ; Return to original position >end flag defined Comments take up space, but if space becomes a problem, you can use the "noformat" primitive to remove comments from your workspace. 2.1.3 Using variables in procedures ----------------------------------- Variables have special capabilities within a procedure. You can use variables to define inputs to a procedure, and to pass information between procedures. In general, it is not good programming practice to bury constants in your procedures. In the following procedure, 40 is a constant: ?to flag >forward 40 >triangle >back 40 >end flag defined Constants do not mean much to someone who reads your procedure later. And because they might appear on more than one line, constants are difficult to change systematically. Using variables instead of constants simplifies your procedures. A variable name can tell a person reading your procedure something about the data object. And to change the data, you need change only the make expression. ?to flag >make "pole 40 >forward :pole >triangle >back :pole >end flag defined To simplify your procedure even further, you can use a variable on a procedure's title line to define an input. ?to flag :pole >forward :pole >triangle >back :pole >end flag defined A variable on the title line makes your procedure require an input. When your procedure is called, Dr. Logo defines a variable that has the name given on the title line. The variable's value is the input object. If no object is input, Dr. Logo complains. ?flag Not enough inputs to flag ?flag 80 ?flag 40 When you give your procedure a variable name as input, Dr. Logo gives the contents of the variable to your procedure. ?make "big 80 ?make "small 40 ?flag :big ?flag :small The next few paragraphs tell how Dr. Logo keeps track of variable definitions. At toplevel, Dr. Logo assigns values to variable names in your workspace. You define variables with make and name expressions directly to the interpreter's ? prompt. These are called "global variables". Dr. Logo keeps track of variables defined by each procedure as it is executing. These are the variables your procedure defines in the title line and with make expressions. Different procedures can have variables that have the same name. Logo programmers sometimes say that variables defined by a procedure are "bound" to their values by that procedure. See the following example. ?make "cookie.jar "snickerdoodle ?to look.in :cookie.jar >print :cookie.jar >end look.in defined ?:cookie.jar snickerdoodle ?look.in "brownie brownie ?:cookie.jar snickerdoodle You can use a variable in your procedure that is not defined by your procedure. At execution time, if the procedure has been called by another procedure, Dr. Logo looks to see if the calling procedure defined the variable. If it finds a definition, it does not look any further. If it does not find a definition, it searches up the levels of calling procedures to toplevel before it complains that the variable is undefined. Because Dr. Logo searches variable bindings this way, you can use variables to pass information between procedures. Usually, the exchange happens this way: the called procedure accesses a variable defined by the calling procedure. It changes the definition of the variable, then returns control to the calling procedure. The calling procedure can then use the information the called procedure stored in the changed variable. The "local" primitive can hide a variable from Dr. Logo's search. If calling and called procedures are using variables of the same name, as is unavoidably the case when a procedure calls itself, a local expression in the called procedure prevents it from altering the calling procedure's value of the variable. An input to a procedure is always local to the procedure. ?to peek.in :cookie.jar >(print "cookie.jar "contains :cookie.j! ar >look.again >end peek.in defined ?to look.again >; cookie.jar not defined here, >; just used! >(print [cookie.jar still contains] :co! okie.jar >end look.again defined ?peek.in "sugar cookie.jar contains sugar cookie.jar still contains sugar ?to peer.in >local "cookie.jar >make "cookie.jar "choc.chip >(print [cookie.jar contains] :cookie.j! ar >look.again >end peer.in defined ?ern "cookie.jar ?:cookie.jar cookie.jar has no value ?peer.in cookie.jar contains choc.chip cookie.jar still contains choc.chip ?look.again cookie.jar still contains ! cookie.jar has no value in look.again: ! (print [cookie.jar still contains] :co ! okie.jar 2.2 Giving inputs to procedures ------------------------------- You can use one or more variables in the title line of a procedure to define inputs to the procedure. Because of this, procedures you define always have a fixed number of inputs. Most primitives also require a fixed number of input objects. However, some primitives can accept a variable number of inputs when the expression is enclosed in parentheses ["(" and ")"]. Without parentheses, these primitives normally require two inputs. With parentheses, they accept more or fewer inputs than are normally required, as shown in the following example. ?(word "sum "mer "sun "shine) summersunshine ?list : favorites Not enough inputs to list ?(list :favorites) [[choc.chip peanut.but oatmeal.raisin ! cream.fill brownie pinwheel shortbread! snickerdoodle]] Most procedures expect a certain kind of input. When you input something to a procedure, it is simply an object, and the variable name is its container. What the procedure does with the object determines what kind of object is required. In fact, a procedure executes normally until it reaches an expression that requires a different kind of input than was supplied. For example, if a procedure requires a number as input, it will not know what to do with a word, and Dr. Logo complains. See the following example and Colorplate 36. ?to pentagon :size >pr [The five angles of a pentagon] >pr [equal 360 / 5 or 72 degrees.] >repeat 5 [fd :size rt 72] >end pentagon defined ?pentagon 40 The five angles of a pentagon equal 360 / 5 or 72 degrees. ?pentagon "forty The five angles of a pentagon equal 360 / 5 or 72 degrees. fd doesn't like forty as input in pent! agon: repeat 5 [fd :size rt 72] As you write procedures that take words and numbers apart and then put them back together, you might create a quoted number such as "123. In general, Dr. Logo accepts a quoted number anywhere an unquoted number is expected. It also accepts an unquoted number where a quoted word is expected. For example, a primitive that expects numbers as input accepts quoted numbers. ?sum "53 "42 95 A primitive that expects a word or list as input accepts unquoted numbers. ?first 9876 9 One exception is the "ascii" primitive. It requires a quoted character as input. "ascii" does not distinguish among numerals, letters, and symbols. ?ascii "2 50 ?ascii 2 ascii doesn't like 2 as input 2.3 Classifying procedures -------------------------- All procedures operate the same way. You use them by following a procedure name with inputs in an expression. However, Logo programmers sometimes find it convenient to classify procedures, that is to say, to group procedures that have something in common together and give the group a name. For example, the procedures that come with Dr. Logo and make up Dr. Logo are called "primitives". Most procedures can be classified as either a command or an operation. A command initiates an action. For example, commands move the turtle, draw pictures, and display text. A command procedure generally ends with "end" or "stop". An operation returns an object: TRUE, FALSE, a word, number, or list. The last expression to be evaluated in an operation procedure is always an output expression. Of course, you can write a procedure that initiates an action before it outputs an object. However, most primitives are simple commands or simple operations. The descriptions in Section 6, "References to Primitives", refer to primitives as operations or commands. Note that the po primitives, which display things on the text screen, are commands, not operations. Commands such as pocall and popkg format lists with spaces and tabs for display on the screen, making the lists inappropriate for input to another procedure. Logo programmers also use classification names to describe kinds of operations. Logical operations such as "and", "not", and "or" return either TRUE or FALSE. An expression that contains a logical operator and, therefore, evaluates to either TRUE or FALSE is called a "predicate expression". Because of this, other logical operation names end with p. For example, ?numberp "two FALSE ?numberp 2 TRUE Other logical operators you can use to form predicate expressions are equalp, emptyp, memberp, listp, and wordp. When you write a procedure that outputs TRUE or FALSE, give the procedure a name that ends with p to indicate that it is a logical operation. Arithmetic operations output numbers. Most arithmetic expressions are formed normally, with the procedure name followed by its inputs. ?product 2 3 6 However, some arithmetic operations are defined by symbols: + - * / ^, instead of names. Some logical operations, called "relational operators", also use symbols: < > =, instead of procedure names. Procedures that use symbols instead of procedure names can be infix operators, which means you can put the symbol between the inputs in the expression. These symbols also work as prefix operators, where the primitive symbol precedes its inputs. ?2 * 3 6 ?= 2 2 TRUE 2.4 Evaluating procedures ------------------------- The Dr. Logo interpreter evaluates one line at a time as you type lines at your keyboard. Dr. Logo also evaluates your procedures one line at a time. When an expression within a procedure begins with the name of a different procedure, Dr. Logo must execute the called procedure before it can return to evaluate the next line of the calling procedure. It must also keep track of where it stopped executing the calling procedure, in case the called procedure calls yet another procedure. To do this, Dr. Logo uses a stack. At toplevel, there is nothing on the stack. During the execution of a procedure, there is one procedure on the stack until it calls another; then, there are two. If the second procedure calls a third, there are three on the stack, and so on. The number of procedures on the stack is sometimes called the level number. The debugging facilities "trace" and "watch" display the level number as procedures execute. Toplevel is level number 0. Dr. Logo assigns part of memory to the stack. Dr. Logo also uses this part of memory to store the values of local variables. If a procedure calls itself and the level number becomes very large, or if the procedure defines a great many local variables, the stack space might fill up. When this occurs, Dr. Logo displays a message and stops executing the procedure. When a procedure is never called by any other procedure, but does call on other procedures itself, Logo programmers classify it as a superprocedure and the procedures it calls as subprocedures. Dr. Logo's potl primitive displays the names of the superprocedures in your workspace. A pocall expression displays the subprocedures called by the input-named procedure. A poref expression displays the procedures that call the input- named procedure. EOF DRLRM3.WS4 (= "Dr. Logo Reference Manual", Section 3) ---------- (Retyped by Emmanuel ROCHE.) Section 3: Editing commands --------------------------- To edit with Dr. Logo means to enter new text, or to change text you have already entered. Editing can be as simple as fixing a typing error in a line you have typed to the interpreter's ? prompt, or as complex as defining several long procedures at once in Dr. Logo's screen editor. Dr. Logo gives you three ways to edit: line editing, procedure editing, and screen editing. You use line editing commands in both procedure and screen editing. Procedure editing is a simple extension of line editing, and screen editing builds on procedure editing. This section tells when, why, and how to use Dr. Logo's line editing, procedure editing, and screen editing commands. You give the commands described in this section to Dr. Logo with control characters, not with expressions. To enter a control character, hold down the control key (marked Ctrl on your keyboard) and press the required letter key. Not all of Dr. Logo's control character commands edit text; some interrupt and terminate procedure execution. The last part of this section introduces Dr. Logo miscellaneous control character commands. 3.1 Line editing ---------------- You can use line editing commands to correct any text you are entering to Dr. Logo. When you write a program that asks the user to type something at the keyboard, the user can also use line editing commands to change his input. The following table summarizes Dr. Logo's line editing control characters. Table 3-1. Line editing control characters Format: Character Effect Ctrl-A Moves the cursor to the beginning of the line. Ctrl-B Moves the cursor [B]ack one character; that is to say, it moves the cursor one position to the left. Ctrl-D [D]eletes the character indicated by the cursor. Ctrl-E Moves the cursor to the [E]nd of the line. Ctrl-F Moves the cursor [F]orward one character; that is to say, it moves the cursor one position to the right. Ctrl-H Deletes the character to the left of the cursor. Ctrl-I [I]nserts a tab (three spaces). Ctrl-K [K]ills the remaining line; that is to say, it deletes all characters right of the cursor to the end of the line. Deleted characters are stored in buffer. Ctrl-Y [Y]anks text from the buffer; that is to say, redisplays line most recently stored in the buffer by an Enter or Ctrl-K keystroke. The following examples show how you can use these control characters when you are entering expressions to the Dr. Logo interpreter. In these examples, the underbar ("_") represents the cursor. Once you have typed a line, you can use control characters to move the cursor left and right over the text. You can make corrections anywhere in the command line. ?repaet 36 [fd 8 lf 10]_ (repeat and lt mistyped) ?r_epaet 36 [fd 8 lf 10] (Ctrl-A to beginning of line) ?repaet_ 36 [fd 8 lf 10] (Ctrl-F to move cursor right) ?rept_ 36 [fd 8 lf 10] (Ctrl-H deletes chars to the left) ?repeat_ 36 [fd 8 lf 10] (ea corrects repeat) ?repeat 36 [fd 8 lf 10]_ (Ctrl-E to end of line) ?repeat 36 [fd 8 lf_ 10] (Ctrl-B moves cursor left) ?repeat 36 [fd 8 l_ 10] (Ctrl-D deletes cursor position) ?repeat 36 [fd 8 lt_ 10] (t corrects lt) You can press the Enter key to send your command to Dr. Logo no matter which character the cursor is indicating in the command line. When you press Enter to send a line to the interpreter, Dr. Logo stores the line in a buffer. You can recall the stored line with Ctrl-Y. This is handy if you want to execute the command again, execute it again with a minor modification, or if you made a typing error and pressed Enter before you corrected it. ?save figures I don't know how to figures ?save figures_ (Ctrl-Y recalls line) ?save "f_igures (Ctrl-B moves cursor left; (" corrects line.) ?save "figures_ (Save file on default drive; Enter then Ctrl-Y recalls line.) ?save "f_igures (Ctrl-B moves cursor left) ?save "b:f_igures (b: to make copy on disk b: Enter) You can delete all or part of a line with a Ctrl-K command. If you have second thoughts, you can recall the deleted characters with Ctrl-Y. ?erns "figure.pack_ (erase names? maybe not...) ?e_rns "figure.pack (Ctrl-A to beginning of line) ?_ (Ctrl-K erases line) ?erns "figure.pack_ (Yes, erase names; Ctrl-Y recalls line) You can also use Ctrl-K and Ctrl-Y to repeat a portion of a command line. ?(pr "I char 3 "N "Y I o N Y ?(pr "I char 3 "N "Y (Ctrl-Y recalls line) ?(pr "_I char 3 "N "Y (Ctrl-B moves cursor left) ?(pr _ (Ctrl-K erases part of line) ?(pr "I char 3 "N "Y_ (Ctrl-Y recalls partial line) ?(pr "I char 3 "N "Y " "I char 3 "N "Y " "I char 3 "N "Y " (Quoted blank spaces and Ctrl-Y keystrokes extend command.) I o N Y I o N Y I o N Y 3.2 Procedure editing --------------------- When you are interacting with the Dr. Logo interpreter, during a pause, or while watching a procedure's executon, you can use the special words "to" and "end" to enter and exit Dr. Logo's procedure editor. For example, when you type a line that begins with "to" to the interpreter's ? prompt, Dr. Logo enters the procedure editor. ?to circle :size >repeat 36 [fd :size rt 10] >end circle defined ? The procedure editor's prompt, >, tells you that Dr. Logo will not immediatelly evaluate the expressions you enter to define the new procedure. Within the procedure editor, you can use any of the line editing control characters commands to move the cursor, correct errors, delete characters and lines, and recall lines. To exit the procedure editor, you must enter the special word "end" by itself as the last line of the procedure. After it reads an end line, Dr. Logo defines the procedure and returns you to the situation from which you entered the procedure editor. 3.3 Screen editing ------------------ To make changes to a defined procedure without reentering the complete procedure definition to the procedure editor, you must use Dr. Logo's screen editor. Using the screen editor, you can move from line to line in a procedure and make changes in each line. You can also load any number of procedures into the screen editor and make changes to each one. In addition, you can use the screen editor to change the contents of variables. The screen editor is smart; that is to say, it makes certain assumptions about your objectives for an editing session. For example, if you define a procedure in the screen editor and forget to enter "end", the screen editor adds an end line to your procedure. When the execution of one of your procedures produces an error message and you call the screen editor, it assumes that you want to edit that procedure, automatically loads that procedure into itself, and positions the cursor at the line in which the error occurred. As with the procedure editor, you can enter the screen editor while interacting with the interpreter, during a pause, or while you are WATCHing the execution of a procedure. You cannot write a procedure that uses the screen editor. Before you can use the screen editor to make changes to your procedures or variables, you must load the ones you want to change into the screen editor's buffer. The screen editor's buffer is its own private workspace. Within the buffer, you can make changes, add text, and delete text. However, the changes you make do not become a part of Dr. Logo's workspace until you exit the screen editor. The changes must become a part of Dr. Logo's workspace before you can save them on disk. There are four primitives that load procedures and variables into the screen editor's buffer and enter the screen editor. All four start with "ed". Each one enters the screen editor; the only difference between these primitives is what they load into the screen editor's buffer. The descriptions of these primitives in Section 6, "References to Primitives", tell what input names these primitives require to load selective groups of procedures and variables into the screen editor's buffer. The following table describes these four primitives. Table 3-2. Load primitives Format: Primitive Purpose edit (ed) Use edit, or its abbreviation ed, to load a procedure or a list of procedures into the screen editor's buffer. If the execution of a procedure has ended with an error message and you immediately enter edit without an input procedure name, the screen editor automatically loads the erroneous procedure into the buffer, and positions the cursor at the offending line. edall Use edall to load both variables and procedures into the screen editor's buffer. "edall" without an input name loads all procedures and variables in Dr. Logo's workspace into the screen editor's buffer. edns Use edns to load a group of variables, names into the screen editor's buffer. "edns" without an input name loads all variables in Dr. Logo's workspace into the screen editor's buffer. edps Use edps to load a group of procedures into the screen editor's buffer. "edps" without an input name loads all procedures in Dr. Logo's workspace into the screen editor's buffer. When you use one of these primitives and enter the screen editor, it clears all normal text from the screen, and displays only the contents of its buffer. The screen editor does not display a prompt character, but the cursor indicates the location that an insertion or control character command will affect. While in the screen editor, you can use all the line editing control characters described in Section 3.1, "Line Editing", to make corrections within lines. The table below summarizes the screen editing control characters you can use to move the cursor from line to line, to page through the buffer, and exit the screen editor. Table 3-3. Screen editing control characters Format: Character Effect Ctrl-C Exits screen editor; updates Dr. Logo's workspace with definitions of all procedures and variables from screen editor's buffer. Ctrl-G Exits screen editor but does not update Dr. Logo's workspace. Any changes made during the screen editing session are discarded. Ctrl-L Readjusts display so that line currently indicated by the cursor is positioned at the center of the screen. If the cursor is less than 12 lines from the beginning of the buffer, the screen editor simply beeps when Ctrl-L is pressed. Ctrl-N Moves the cursor to the [N]ext line; the cursor moves down one line towards the end of the buffer. Ctrl-O [O]pens a new line. A Ctrl-O keystroke is equivalent to pressing Enter followed by Ctrl-B. Ctrl-P Moves cursor to the [P]revious line; the cursor moves up one line towards the beginning of the buffer. Ctrl-V Displays the next screenfull of text in the screen editor's buffer, the next 24 lines towards the bottom of the buffer. ESC-V Displays the previous screenfull of text in the screen editor's buffer, the previous 24 lines towards the beginning of the buffer. ESC-< Positions the cursor at the beginning of the screen editor's buffer. ESC-> Positions the cursor at the end of the screen editor's buffer. The following examples show how you can combine these screen editing control characters with line editing control characters for editing shortcuts. Several combinations of control character commands are convenient and worth remembering. Ctrl-E Ctrl-D deletes the Carriage Return between two lines and makes them into one line. Ctrl-A Ctrl-K deletes the line currently indicated by the cursor. You can combine Ctrl-O with Ctrl-Y and Ctrl-K to quickly move a line within the screen editor. The line moved below makes the countdown procedure print a 0 before it stops. The edit is performed with only eight control character commands. ?countdown 4 4 3 2 1 ?ed "countdown (editor clear screen) to countdown :number_ if :number = 0 [stop] pr :number countdown :number - 1 end (Ctrl-N Ctrl-A positions cursor at line to be moved) to countdown :number i_f :number = 0 [stop] pr :number countdown :number - 1 end (Ctrl-K deletes line) to countdown :number _ pr :number countdown :number - 1 end (Ctrl-N positions cursor at new location) to countdown :number pr :number c_ountdown :number - 1 end (INS Ctrl-Y inserts line) to countdown :number pr :number i_f :number = 0 [stop] countdown :number - 1 end (Ctrl-C defines procedure.) countdown defined ?countdown 4 4 3 2 1 0 ? The paging control character commands become useful when you have more than 24 lines of text in the screen editor's buffer. You can enter edall to load everything from Dr. Logo's workspace into the screen editor's buffer, then experiment with Ctrl-L, Ctrl-V, ESC-V, ESC-<, and ESC->. To exit the screen editor normally, press Ctrl-C. In this case, Dr. Logo updates the definitions of procedures and variables in its workspace with the definitions from the screen editor's buffer. If you have modified the title line of a procedure, Dr. Logo defines a new procedure and does not change the original definition of the procedure currently in the workspace. If you omitted an end line at the end of a procedure, Dr. Logo adds one as it updates its workspace. To discard the changes you have made during an editing session, exit the screen editor with Ctrl-G. This leaves Dr. Logo's workspace in the same condition you found it when you entered the screen editor. When you exit the screen editor, Dr. Logo returns you to the same situation from which you entered. For example, if you entered the screen editor during a pause in a procedure, Dr. Logo returns to the appropriate pause prompt and waits for your next command. In a certain situation, you can use a few screen editing commands outside the screen editor. This situation occurs when you are entering a long expression outside the screen editor and Dr. Logo prints a "!" before starting on the next line. In this case, you can use Ctrl-P and Ctrl-N to move up and down between lines. You can also use Ctrl-O to open a new line, but all characters right of the Ctrl-O keystroke are ignored; Dr. Logo treats the Ctrl-O as the end of the expression. However, the characters are not lost. You can recall them with Ctrl-Y. 3.4 Other control character commands ------------------------------------ Dr. Logo recognizes several control character commands for actions other than line editing. In fact, the only control characters that have no meaning for Dr. Logo are Ctrl-U, Ctrl-J, Ctrl-R, and Ctrl-X. The remaining control characters terminate and interrupt procedure execution and scrolling screen displays, and switch between a full graphics screen, a full text screen, and a split screen. Section 4, "Text and Graphic Screens", describes screen control character commands in detail. The following table summarizes the miscellaneous control character commands. Table 3-4. Additional control character commands Format: Character Effect Ctrl-G Immediately terminates the currently executing procedure. Ctrl-L Displays a full graphics screen; devotes the monitor to turtle graphics. Ctrl-M Carriage Return; same as pressing the Enter key. Ctrl-Q Generates the [Q]uoting character ("\") that makes Dr. Logo treat a delimiter character as a literal character. Ctrl-S Displays a [S]plitscreen; divides the monitor between a partial graphic screen and a text window. Ctrl-T Displays a full [T]ext screen; devotes the monitor to text. Ctrl-W Interrupt the scrolling of a text display; [W]aits until the next keystroke to continue the display. Ctrl-Z Interrupts the currently executing procedure, displays pause prompt to allow interactive debugging. Enter "co" to continue execution of interrupted procedure. EOF DRLRM4.WS4 (= "Dr. Logo Reference Manual", Section 4) ---------- (Retyped by Emmanuel ROCHE.) Section 4: Text and graphic screens ----------------------------------- One of Dr. Logo's most exciting capabilities on your IBM Personal Computer is to create graphic designs and display text in many beautiful colors. Dr. Logo shows you a graphics cursor called "the turtle", which dutifully draws designs according to your instructions. However, this section does not tell you how to control the turtle; it tells you how to control the physical properties of your display. It tells what combinations of text and graphics are possible, how to switch between text and graphic screens, and how to control the colors of drawings and text. 4.1 Monitors, screens, and windows ---------------------------------- In memory, Dr. Logo maintains two screens: a text screen and a graphic screen. A text screen contains only text, with up to 80 characters in one line. The text screen never contains more than 25 lines. A graphic screen can contain drawings and text, but can have only 40 characters in one line. The graphic screen potentially extends beyond the range of your monitor. The portion of the graphic screen your monitor can display is called "the visual field". Dr. Logo maintains these complete screens in memory, so that it can display combinations of parts of them on your monitor and restore the full display of either screen. You control what combination of text and graphics appears on your monitor with Dr. Logo primitives and control character commands. Your color monitor can display both text and graphic screens. A monochrome monitor can display only the text screen. To let you see the text of your procedures, or your interaction with the interpreter, without devoting your entire monitor to screen, Dr. Logo can direct part of the text screen into a text window. When a window of text appears on the graphic screen, the combination of text and graphics is called "a splitscreen". When you enter "debug", Dr. Logo divides the monitor into two text windows, then directs text displayed by a procedure to the lower PROGRAM window, and text displayed by debugging facilities to the upper DEBUG window. 4.2 Displaying text and graphic screens --------------------------------------- Dr. Logo supports both primitives and control character commands that make your monitor display the text screen and the graphic screen in various combinations, as described in the following table. Table 4-1. Displaying screens Format: Control character Primitive Display Ctrl-L fullscreen Displays a full graphic screen; devotes the monitor to graphics. Ctrl-S splitscreen Displays a splitscreen; divides the monitor between a partial graphic screen and a text window. Ctrl-T textscreen Displays a full text screen; devotes the monitor to text. (no control character) debug Displays two text windows on the monitor. (no control character) nodebug Closes text windows, returns monitor to a cleared full text screen. The control character commands are the quickest way to switch displays while you are interacting with the interpreter. Use the fullscreen, splitscreen, and textscreen primitives when you want to switch displays within a procedure. You must always use debug and nodebug to control the two debugging text windows. "debug" disables Ctrl-S and splitscreen; you cannot display a splitscreen while you are using the debugging text windows. "nodebug" restores Ctrl-S and splitscreen. When you are using one color monitor, Dr. Logo automatically displays a splitscreen when you enter a command that moves the turtle. However, Dr. Logo can support both a color and a monochrome monitor. When you have two monitors, Dr. Logo automatically displays the text screen on the monochrome monitor, and the graphic screen on the color monitor. Having two monitors changes the way some of the display control primitives work. When you have two monitors, Dr. Logo does not automatically display a splitscreen when you enter a graphics command because full graphic and text screens are always displayed. However, you can use Ctrl-S and splitscreen to open a text window on the graphic screen. To remove the splitscreen text window and display the full text screen on the monochrome monitor, you can use fullscreen, Ctrl-L, or Ctrl-T. If you use textscreen at any time on a two monitor system, Dr. Logo displays the text screen on the color monitor. 4.3 Text screen --------------- The text screen has positions for 2000 text characters: 25 lines of text with 80 characterrs in each line. The coordinate system shown below references these characters. A text coordinate list contains two numbers: the first is the row or character number, and the second is the line number. [0 0] [79 0] +-----------------------+ | | | | | | | | | | +-----------------------+ [0 24] [79 24] You use this coordinate system with "setcursor" to position the cursor within the text screen. Dr. Logo lets you control the foreground and background color of each character cell. "textbg" sets the background of the text screen to the color represented by the input number. There are eight possible colors, so normally you input a number in the range 0 to 7. However, textbg also controls whether or not the foreground characters blink. To display blinking characters, input a number between 8 and 15 to textbg, as shown in the following table. Table 4-2. Background colors Normal Blinking Background color ------ -------- ---------------- 0 8 Black 1 9 Blue 2 10 Green 3 11 Cyan 4 12 Red 5 13 Magenta 6 14 Brown 7 15 Grey "textfg" sets the foreground of the text screen to the color represented by the input number. The IBM Personal Computer supports 16 foreground colors, but if your color monitor does not support two levels of intensity, you can see only the first eight colors listed in the following table. Table 4-3. Foreground colors Input Foreground Input Foreground number colors number colors ------ ---------- ------ ---------- 0 Black 8 Black 1 Blue 9 Bright blue 2 Green 10 Bright green 3 Cyan 11 Bright cyan 4 Red 12 Bright red 5 Magenta 13 Bright magenta 6 Brown 14 Yellow 7 Grey 15 White 4.4 Graphic screen ------------------ Dr. Logo gives you complete control of the 60,000 individual dots that make up the visual field of your graphic screen; there are 300 dots horizontally and 200 dots vertically. Technically, these dots are called "pixels". A turtle step is equivalent to one dot. For example, when you enter "forward 1", the turtle moves forward one pixel. The dots make any diagonal lines the turtle draws seem jagged. Although Dr. Logo calculates angles and headings with great precision, the turtle rounds to the nearest degree before drawing. 4.4.1 Graphic coordinates and the visual field ---------------------------------------------- You can reference each dot on the graphic screen individually by its coordinates. Using coordinates, you can quickly move the turtle to any location on the screen (setpos), or change any single dot to the turtle's current pencolor (dot). A graphic screen coordinate list contains two numbers: an x coordinate indicates the horizontal position, and a y coordinate indicates the vertical position. For example, the coordinates of the turtle's home position are [0 0], the center of the screen. To reference a dot in the visual graphic field, the x coordinate can be in the range -160 to +159, and the y coordinate can be in the range -99 to +100. [-160 100] [159 100] +-----------------------+ | | | | | [0 0] | | | | | +-----------------------+ [-160 -99] [159 -99] When you first start Dr. Logo, the visual field is just a window on a greater graphics plane. You can use numbers outside the visual coordinate ranges to reference positions outside the visual field; the turtle can draw a part of a design off the monitor and return. You can limit the turtle to the visual field with two primitives: fence and wrap. "fence" sets a boundary around the edge of the visual field. When the turtle encounters the boundary, Dr. Logo complains "Turtle out of bounds" and stops any executing procedure. "wrap" makes the turtle reappear on the opposite side of the monitor when it exceeds the boundary. Use "window" to remove the boundary. 4.4.2 Graphic text coordinates ------------------------------ On the graphic screen, there are positions of 1000 text characters: 25 lines of text with 40 characters per line. The coordinate system shown below references these character cells. In a text coordinate list, the first number is the row or character number, and the second number is the line number. [0 0] [39 0] +-----------------------+ | | | | | | | | | | +-----------------------+ [0 24] [39 24] You can use this coordinate system to position the cursor within the splitscreen text window (setcursor), or to take input from a lightpen (lpen). When you use "turtletext" to display text on the graphic screen, the first character of the input object appears in the first character cell to the right of the turtle's center line. The character might not appear directly under the turtle if the turtle is not on a character cell boundary. 4.4.3 Graphic colors -------------------- Although your color monitor can display many different colors, the graphic screen can contain only four colors at any one time. In Dr. Logo, the number you input to setbg specifies with set of four colors you want your monitor to display. First, you have to select a background color. The IBM Personal Computer supports eight background colors in two levels of intensity, although your color monitor might not display different intensities. The numbers setbg accepts select background colors as described in the following table. Table 4-4. Background color intensity Low intensity High intensity ----------------- ------------------ 0 16 32 48 Black 8 24 40 56 Black 1 17 33 49 Blue 9 25 41 57 Blue 2 18 34 50 Green 10 26 42 58 Green 3 19 35 51 Cyan 11 27 42 59 Cyan 4 20 36 52 Red 12 28 43 60 Red 5 21 37 53 Magenta 13 29 45 61 Magenta 6 22 38 54 Yellow 14 30 46 62 Yellow 7 23 40 55 White 15 31 47 63 White Each of the four numbers for a background color specifies a different pen for the turtle to use. The turtle has four pens. Each pen has four unique colors of ink, one of which is the background color that the turtle uses for erasing. Use setpc to select the pen's ink color. When the background color is in the range 0 to 15, - setpc 1 selects dark green ink - setpc 2 selects dark red ink - setpc 3 selects dark yellow ink When the background color is in the range 16 to 31, - setpc 1 selects bright green ink - setpc 2 selects bright red ink - setpc 3 selects bright yellow ink When the background color is in the range 32 to 47, - setpc 1 selects dark cyan ink - setpc 2 selects dark magenta ink - setpc 3 selects dark grey ink When the background color is in the range 48 to 63, - setpc 1 selects bright cyan ink - setpc 2 selects bright magenta ink - setpc 3 selects bright white ink For all background color numbers, setpc 0 selects background color (erasing) ink. When Dr. Logo first starts up, the background color is 1, and the pencolor number is 2. 4.4.4 Graphic text color ------------------------ "textbg" controls the background color of the text on the graphic screen, both the splitscreen text window and characters typed by turtletext. The background color of graphic text can be any one of the four colors of the turtle's current pen. For example, the following table shows how a textbg command affects the graphic text when the background of the graphic screen is set to 1 (blue) and the four pencolors are blue, green, red, and yellow. Table 4-5. Background color of graphic text textbg number Graphic text background ------------- ----------------------- 0, 4, 8, 12 Blue 1, 5, 9, 13 Green 2, 6, 10, 14 Red 3, 7, 11, 15 Yellow Unlike the text screen, when you input a number greater than seven to textbg, graphic screen text characters are not affected. Characters on the graphic screen cannot blink. "textfg" controls the foreground color of graphic text. The characters in the splitscreen text window and the turtletext characters can be one of the four colors of the turtle's current pen. For example, the following table shows how a textfg command colors the graphic screen characters when the background of the graphic screen is set to 1 (blue) and the four pencolors are blue, green, red, and yellow. Table 4-6. Foreground color of graphic text textfg number Graphic text color ------------- ------------------ 0, 4, 8, 12 Blue 1, 5, 9, 13 Green 2, 6, 10, 14 Red 3, 7, 11, 15 Yellow EOF DRLRM5.WS4 (= "Dr. Logo Reference Manual", Section 5) ---------- (Retyped by Emmanuel ROCHE.) Section 5: Property lists, workspace, and disks ----------------------------------------------- Storage is one of Dr. Logo's most important resources. There are two kinds of storage: temporary storage and permanent storage. When you enter procedure and variable definitions at your keyboard, they are temporarily stored in a part of your computer's memory called "the workspace". To record your procedures permanently, you must save them on disk. To help organize your workspace and disk files, Dr. Logo lets you bundle procedures and variables into packages. Dr. Logo does this by adding system properties to an object's property list. This section tells how to use property lists and packages, how to organize your workspace for best performance, and how to create, copy, rename, and erase disk files. 5.1 Property lists ------------------ Any object in the workspace can have a property list. In fact, Dr. Logo uses property lists to create variables, procedures, and packages. A property list is made up of property pairs. The first element of a property pair is the property name; the second element is its value. You can assign your own properties to an object. Property lists make it simple to store and retrieve information, as shown in the following example. ?pprop "Kathy "ext 42 ?pprop "Meryle "ext 58 ?pprop "Ellen "ext 66 ?pps Kathy's ext is 42 Meryle's ext is 58 Ellen's ext is 66 You can create whatever property pairs are appropriate to your application. Dr. Logo adds or removes property pairs when you use primitives identified in the following table. Do not use system property names for purposes other than those listed in the table. Table 5-1. Property pairs Property name Primitive Property value ------------- ----------- -------------- .APV make, name, The value of a global variable ern, erall, erns .BUR bury, unbury When TRUE, the package is buried .CAT catch, throw Catch descriptor .DEF to, define, The definition of a procedure er, erall, erps .ENL to, ed End of a procedure line that is broken by a Carriage Return and spaces or tabs. .FMT to, ed Beginning of a procedure line that is broken by a Carriage Return and spaces or tabs. .FUN Identifies an active function, a function in the process of being evaluated. .PAK package The name of the package to which this object belongs. .PAR The parameters of an active function .PAU Pause .PKG package When TRUE, object is a package name .PRM Memory location of the primitive .REM Remark or comment that follows a semicolon .SPC Number of spaces that follow a Carriage Return in a broken procedure line. When you use plist to display property lists, you will always see an .APV pair in a variable name's property list, and a .DEF pair in a procedure's property lists. For example, ?make "flavor "chocolate ?plist "flavor [.APV chocolate] ?to eat.cookie >pr [yum yum!] >end eat.cookie defined ?plist "eat.cookie [.DEF [[] [pr [yum yum!]]]] However, you might never see some of the pairs listed above in a property list. This is because Dr. Logo puts properties such as during the procedure's execution. 5.2 Managing your workspace --------------------------- Your workspace is the part of your computer's memory that Dr. Logo allocates for the temporary storage of your procedures and variables. This section tells how Dr. Logo measures your workspace, and how you can use packages to organize your workspace. 5.2.1 Measuring your workspace ------------------------------ Dr. Logo measures your workspace in nodes. A node is equivalent to five bytes, and can hold five characters. In general, the more workspace you have, the better your procedures will perform. You can check how many free nodes there are in your workspace at any time with the "nodes" primitive. Try nodes immediately after you start Dr. Logo, to see the maximum size of your workspace. If you have enough memory in your IBM Personal Computer, you can have over 10,000 nodes at start-up. If you use "noprim" to remove the poprim information from the workspace, you add approximately 600 nodes to the maximum size of your workspace. You tie up nodes in your workspace by entering procedures and other objects at the keyboard, or reading them in from disk with "load". Dr. Logo also adds to the contents of the workspace by making copies of local variables and recursive procedures during a procedure's execution. 5.2.2 Garbage collection ------------------------ Dr. Logo does not automatically throw out these copies of local variables and recursively-called procedures after a procedure finishes execution. However, when there are fewer than 200 free nodes in your workspace, a part of Dr. Logo called "the garbage collector" sorts through the workspace and erases any copies of variables or procedures that are no longer needed. You might occasionally see an executing procedure hesitate for a few moments while the garbage collector does its work. You can call the garbage collector with the "recycle" primitive. If you use recycle to clean up the workspace before initiating a time-critical procedure, you minimize the chance that the garbage collector will interrupt the execution of the procedure. Try using "nodes" before and after "recycle" to learn how many nodes are taken up by the temporary copies of variables and procedures. The garbage collector uses the stack as it sorts objects in your workspace. Although Dr. Logo allocates stack space dynamically, if garbage collection occurs during the execution of a recursive procedure or other situation where the stack is heavily used, the garbage collector can run out of stack space. When this occurs, Dr. Logo displays a message and stops executing the procedure. When workspace becomes critical because there are fewer than 400 free nodes, Dr. Logo displays an exclamation point prompt ("!"). In this situation, enter "recycle" immediately. If, after "recycle", you still have fewer than 600 nodes, it is time to reorganize your procedures, save some of them on disk, and remove them from the workspace, to give the remaining procedures room to execute. You can use "load" within a procedure to restore saved procedures to the workspace when they are needed. 5.2.3 Packages -------------- Packages help you organize your workspace. When you put related procedures and variables in a package, you can display, edit, save, and erase those procedures and variables as a group separate from other procedures and variables in the workspace. Use "package" to create a package or add items to a package. "package" requires two inputs. The first is the name of the package. You can give "package" either a name or a list of names of items to be placed in the package as the second input. The list can contain a mixture of variable and procedure names. For example, ?package "cookies "flavor ?package "cookies [eat.cookies flavor] "popkg" displays the name and contents of each package defined in the workspace, as shown in the following example. ?popkg cookies "flavor eat.cookies When you input a package name to one of the following primitives, it takes action only on the procedures and variables contained in the package. edall erall glist pops save edns erns poall pots edps erps pons pps If you do not specify a package name to these primitives, they act on all procedures and variables in the workspace, except for those in buried packages. A buried package is hidden from the primitives listed above. To bury a package, use "bury", as shown in the following example. ?bury "cookies ?popkg cookies is buried "flavor eat.cookies Dr. Logo creates and buries packages by adding system properties to property lists. It adds the .PAK property with the name of the package to the packaged procedure's or variable's property list. It adds the .PAK property with the value TRUE to the package name's property list. When you bury a package, Dr. Logo adds the .BUR property with the value TRUE to the package name's property list. The primitives listed above that can take a package name as input check the property list of the package name for the .BUR property before taking action. 5.3 Drives, disks, and files ---------------------------- When you turn off your computer, all the procedures and variables in your workspace are lost. So, before you turn your computer off, you must save them on a more permanent medium, a disk. Dr. Logo stores information on disk in files, and gives each file the name you specify. The part of your computer that reads and writes file on a disk is called a "drive". This section gives some background information on drives, disks, and files. Many of the primitives that copy and erase disks and files display a message that asks you to confirm that you do, indeed, want to copy or erase before the primitive proceeds. This is because it is sometimes too easy to erase or copy over important files by mistake. However, such messages make it inconvenient to use these primitives from within a procedure. The system variable NOACK controls whether or not these primitives display a message. Make NOACK TRUE to suppress the messages. 5.3.1 Drives ------------ Your IBM Personal Computer has one or two drives. A drive can be either single- or double-sided, which means the drive can write on one or both sides of the disk. If your drive can write on both sides of the disk, you can store twice as much information on a disk. When you first start Dr. Logo, it makes drive A: the default drive. This means that, until you tell Dr. Logo to do otherwise, it looks for information on the disk in drive A:. If you have a single-drive system, drive A: will always be your default drive. If you have more than one drive, you can tell Dr. Logo to change the default drive with a "setd" command. "defaultd" outputs the name of the default drive in uppercase. ?defaultd A: ?setd "b: ?defaultd B: Before you can save anything on disk, you must put a formatted disk in a drive. You cannot save information on your Dr. Logo system disk, so if you have a one-drive system, you must remove the Dr. Logo system disk from the drive and insert a data disk. To tell Dr. Logo that you have inserted a new disk, enter "resetd". If you try to save information on a newly-inserted disk without entering "resetd", Dr. Logo will complain. 5.3.2 Disks ----------- Dr. Logo cannot save information on a disk that is fresh from the box. The disk must be initialized or formatted to single- or double-sided. During the initialization process, Dr. Logo tests and prepares one or both surfaces of the disk for future load and save operations. Appendix E, "Getting Started", and the description of "initd" in Section 6, "References to Primitives", both tell how to initialize a disk. Dr. Logo measures the space on your disk in bytes, not nodes. "spaced" outputs the number of free bytes on the disk in the specified drive. A single-sided disk can hold 150,000 bytes. A double-sided disk can hold 300,000 bytes. 5.3.3 Files ----------- A file is a set of related information stored on disk. A Dr. Logo file contains objects such as procedures and variables with their property lists. You can create a Dr. Logo file with "save". Dr. Logo saves either everything in the workspace, or just the objects you specify with packages. Dr. Logo gives the file the name you specify by writing the name in the disk's directory. The name you specify cannot contain more than eight characters. If you specify a name longer than eight characters, Dr. Logo uses the first eight characters as the name. You can change a file's name with "changef", copy a file with "copyf", and erase a file with "erf". "getfs" outputs a list of the Dr. Logo file names on the disk in the default or specified drive. Like drive names, Dr. Logo outputs file names in uppercase. "erf" and "getfs" can accept an ambiguous file name as input. An ambiguous file name can reference more than one file, because it contains a wildcard character and gives Dr. Logo a pattern to match. The wildcard character is the question mark ("?"), which must be the last character in the file name. ?getfs [SHAPES PIGLATIN PLAID] ?getfs "p? [PIGLATIN PLAID] EOF