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XLISP: An Experimental Object Oriented Language Version 1.2 October 11, 1984 by David Betz 114 Davenport Ave. Manchester, NH 03103 (603) 625-4691 (home) XLISP: An Experimental Object Oriented Language Page 2 TABLE OF CONTENTS 1.0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . 3 2.0 A NOTE FROM THE AUTHOR . . . . . . . . . . . . . . . 4 3.0 XLISP COMMAND LOOP . . . . . . . . . . . . . . . . . 5 4.0 DATA TYPES . . . . . . . . . . . . . . . . . . . . . 6 5.0 THE EVALUATOR . . . . . . . . . . . . . . . . . . . 7 6.0 LEXICAL CONVENTIONS . . . . . . . . . . . . . . . . 8 7.0 OBJECTS . . . . . . . . . . . . . . . . . . . . . . 9 8.0 SYMBOLS . . . . . . . . . . . . . . . . . . . . . 12 9.0 EVALUATION FUNCTIONS . . . . . . . . . . . . . . . 13 10.0 SYMBOL FUNCTIONS . . . . . . . . . . . . . . . . . 14 11.0 PROPERTY LIST FUNCTIONS . . . . . . . . . . . . . 15 12.0 LIST FUNCTIONS . . . . . . . . . . . . . . . . . . 16 13.0 DESTRUCTIVE LIST FUNCTIONS . . . . . . . . . . . . 18 14.0 PREDICATE FUNCTIONS . . . . . . . . . . . . . . . 19 15.0 CONTROL FUNCTIONS . . . . . . . . . . . . . . . . 20 16.0 ARITHMETIC FUNCTIONS . . . . . . . . . . . . . . . 22 17.0 BITWISE LOGICAL FUNCTIONS . . . . . . . . . . . . 23 18.0 RELATIONAL FUNCTIONS . . . . . . . . . . . . . . . 24 19.0 STRING FUNCTIONS . . . . . . . . . . . . . . . . . 25 20.0 INPUT/OUTPUT FUNCTIONS . . . . . . . . . . . . . . 26 21.0 FILE I/O FUNCTIONS . . . . . . . . . . . . . . . . 27 22.0 SYSTEM FUNCTIONS . . . . . . . . . . . . . . . . . 28 XLISP: An Experimental Object Oriented Language Page 3 INTRODUCTION 1.0 INTRODUCTION XLISP is an experimental programming language combining some of the features of LISP with an object oriented extension capability. It was implemented to allow experimentation with object oriented programming on small computers. There are currently implementations running on the PDP-11 under RSX-11, RT-11, and UNIX V7, on the VAX-11 under VAX/VMS and Berkeley VAX/UNIX, on the Z-80 under CP/M-80, on the Z8000 under UNIX V7, and on the 8088/8086 under CP/M-86 or MS-DOS. A version is currently being developed for the 68000 under CP/M-68K. It is completely written in the programming language 'C' and is easily extended with user written built-in functions and classes. It is available in source form free of charge to non-commercial users. Prospective commercial users should contact the author for permission to use XLISP. Many traditional LISP functions are built into XLISP. In addition, XLISP defines the objects 'Object' and 'Class' as primitives. 'Object' is the only class that has no superclass and hence is the root of the class heirarchy tree. 'Class' is the class of which all classes are instances (it is the only object that is an instance of itself). This document is intended to be a brief description of XLISP. It assumes some knowledge of LISP and some understanding of the concepts of object oriented programming. Version 1.2 of XLISP differs from version 1.1 in several ways. It supports many more Lisp functions. Also, many version 1.1 functions have been renamed and/or changed slightly to follow traditional Lisp usage. One of the most frequently reported problems in version 1.1 resulted from many functions being named after their equivilent functions in the C language. This turned out to be confusing for people who were trying to learn XLISP using traditional LISP texts as references. Version 1.2 renames these functions to be compatible with more traditional dialects of LISP. A recommended text for learning LISP programming is the book "LISP" by Winston and Horn and published by Addison Wesley. The first edition of this book is based on MacLisp and the second edition is based on Common Lisp. Future version of XLISP will migrate towards compatiblility with Common Lisp. XLISP: An Experimental Object Oriented Language Page 4 A NOTE FROM THE AUTHOR 2.0 A NOTE FROM THE AUTHOR If you have any problems with XLISP, feel free to contact me for help or advice. Please remember that since XLISP is available in source form in a high level language, many users have been making versions available on a variety of machines. If you call to report a problem with a specific version, I may not be able to help you if that version runs on a machine to which I don't have access. If you find a bug in XLISP, first try to fix the bug yourself using the source code provided. If you are successful in fixing the bug, send the bug report along with the fix to me. If you don't have access to a C compiler or are unable to fix a bug, please send the bug report to me and I'll try to fix it. Any suggestions for improvements will be welcomed. Feel free to extend the language in whatever way suits your needs. However, PLEASE DO NOT RELEASE ENHANCED VERSIONS WITHOUT CHECKING WITH ME FIRST!! I would like to be the clearing house for new features added to XLISP. If you want to add features for your own personal use, go ahead. But, if you want to distribute your enhanced version, contact me first. Please remember that the goal of XLISP is to provide a language to learn and experiment with LISP and object oriented programming on small computers. Version 1.2 barely fits on a 64K Z-80 running CP/M-80. XLISP: An Experimental Object Oriented Language Page 5 XLISP COMMAND LOOP 3.0 XLISP COMMAND LOOP When XLISP is started, it first tries to load "init.lsp" from the default directory. It then loads any files named as parameters on the command line (after appending ".lsp" to their names). It then issues the following prompt: > This indicates that XLISP is waiting for an expression to be typed. When an incomplete expression has been typed (one where the left and right parens don't match) XLISP changes its prompt to: n> where n is an integer indicating how many levels of left parens remain unclosed. When a complete expression has been entered, XLISP attempts to evaluate that expression. If the expression evaluates successfully, XLISP prints the result of the evaluation and then returns to the initial prompt waiting for another expression to be typed. Input can be aborted at any time by typing the CONTROL-G key (it may be necessary to follow CONTROL-G by return). XLISP: An Experimental Object Oriented Language Page 6 DATA TYPES 4.0 DATA TYPES There are several different data types available to XLISP programmers. o lists o symbols o strings o integers o objects o file pointers o subrs/fsubrs (built-in functions) Another data type is the stream. A stream is a list node whose car points to the head of a list of integers and whose cdr points to the last list node of the list. An empty stream is a list node whose car and cdr are nil. Each of the integers in the list represent characters in the stream. When a character is read from a stream, the first integer from the head of the list is removed and returned. When a character is written to a stream, the integer representing the character code of the character is appended to the end of the list. When a function indicates that it takes an input source as a parameter, this parameter can either be an input file pointer or a stream. Similarly, when a function indicates that it takes an output sink as a parameter, this parameter can either be an output file pointer or a stream. XLISP: An Experimental Object Oriented Language Page 7 THE EVALUATOR 5.0 THE EVALUATOR The process of evaluation in XLISP: o Integers, strings, objects, file pointers, and subrs evaluate to themselves o Symbols evaluate to the value associated with their current binding o Lists are evaluated by evaluating the first element of the list o If it evaluates to a subr, the remaining list elements are evaluated and the subr is called with these evaluated expressions as arguments. o If it evaluates to an fsubr, the fsubr is called using the remaining list elements as arguments (they are evaluated by the subr itself if necessary) o If it evaluates to a list and the car of the list is 'lambda', the remaining list elements are evaluated and the resulting expressions are bound to the formal arguments of the lambda expression. The body of the function is executed within this new binding environment. o If it evaluates to a list and the car of the list is 'nlambda', the remaining list elements are bound to the formal arguments of the nlambda expression. The body of the function is executed within this new binding environment. o If it evaluates to an object, the second list element is evaluated and used as a message selector. The message formed by combining the selector with the values of the remaining list elements is sent to the object. XLISP: An Experimental Object Oriented Language Page 8 LEXICAL CONVENTIONS 6.0 LEXICAL CONVENTIONS The following conventions are followed when entering XLISP programs: Comments in XLISP code begin with a semi-colon character and continue to the end of the line. Symbol names in XLISP can consist of any sequence of non-blank printable characters except the following: ( ) . ' " ; Upper and lower case characters are distinct. The symbols 'CAR' and 'car' are not the same. The names of all built-in functions are in lower case. The names of all built-in objects are lower case with an initial capital. Symbol names must not begin with a digit. Integer literals consist of a sequence of digits optionally beginning with a '+' or '-'. The range of values an integer can represent is limited by the size of a C 'int' on the machine that XLISP is running on. Literal strings are sequences of characters surrounded by double quotes. Within quoted strings the '\' character is used to allow non-printable characters to be included. The codes recognized are: \\ means the character '\' \n means newline \t means tab \r means return \e means escape \nnn means the character whose octal code is nnn The single quote character can be used as a shorthand for a call on the function 'quote': 'foo is equivalent to: (quote foo) XLISP: An Experimental Object Oriented Language Page 9 OBJECTS 7.0 OBJECTS Definitions: o selector - a symbol used to select an appropriate method o message - a selector and a list of actual arguments o method - the code that implements a message Since XLISP was created to provide a simple basis for experimenting with object oriented programming, one of the primitive data types included was 'object'. In XLISP, an object consists of a data structure containing a pointer to the object's class as well as a list containing the values of the object's instance variables. Officially, there is no way to see inside an object (look at the values of its instance variables). The only way to communicate with an object is by sending it a message. When the XLISP evaluator evaluates a list the value of whose first element is an object, it interprets the value of the second element of the list (which must be a symbol) as the message selector. The evaluator determines the class of the receiving object and attempts to find a method corresponding to the message selector in the set of messages defined for that class. If the message is not found in the object's class and the class has a super-class, the search continues by looking at the messages defined for the super-class. This process continues from one super-class to the next until a method for the message is found. If no method is found, an error occurs. When a method is found, the evaluator binds the receiving object to the symbol 'self', binds the class in which the method was found to the symbol 'msgclass', and evaluates the method using the remaining elements of the original list as arguments to the method. These arguments are always evaluated prior to being bound to their corresponding formal arguments. The result of evaluating the method becomes the result of the expression. XLISP: An Experimental Object Oriented Language Page 10 OBJECTS Classes: Object THE TOP OF THE CLASS HEIRARCHY Messages: show SHOW AN OBJECT'S INSTANCE VARIABLES returns the object class RETURN THE CLASS OF AN OBJECT returns the class of the object isnew THE DEFAULT OBJECT INITIALIZATION ROUTINE returns the object sendsuper <sel> [<args>...] SEND SUPERCLASS A MESSAGE <sel> the message selector <args> the message arguments returns the result of sending the message XLISP: An Experimental Object Oriented Language Page 11 OBJECTS Class THE CLASS OF ALL OBJECT CLASSES (including itself) Messages: new CREATE A NEW INSTANCE OF A CLASS returns the new class object isnew [<scls>] INITIALIZE A NEW CLASS <scls> the superclass returns the new class object answer <msg> <fargs> <code> ADD A MESSAGE TO A CLASS <msg> the message symbol <fargs> the formal argument list this list is of the form: (<farg>... [&rest <rarg>] [&aux <aux>...]) where <farg> a formal argument <rarg> bound to the rest of the arguments <aux> a auxiliary variable <code> a list of executable expressions returns the object ivars <vars> DEFINE THE LIST OF INSTANCE VARIABLES <vars> the list of instance variable symbols returns the object cvars <vars> DEFINE THE LIST OF CLASS VARIABLES <vars> the list of class variable symbols returns the object When a new instance of a class is created by sending the message 'new' to an existing class, the message 'isnew' followed by whatever parameters were passed to the 'new' message is sent to the newly created object. When a new class is created by sending the 'new' message to the object 'Class', an optional parameter may be specified indicating the superclass of the new class. If this parameter is omitted, the new class will be a subclass of 'Object'. A class inherits all instance variables, class variables, and methods from its super-class. XLISP: An Experimental Object Oriented Language Page 12 SYMBOLS 8.0 SYMBOLS o self - the current object (within a message context) o msgclass - the class in which the current method was found o *oblist* - the object list o *standard-input* - the standard input file o *standard-output* - the standard output file o *tracenable* - flag controlling trace back printout on errors o *unbound* - indicator for unbound symbols XLISP: An Experimental Object Oriented Language Page 13 EVALUATION FUNCTIONS 9.0 EVALUATION FUNCTIONS (eval <expr>) EVALUATE AN XLISP EXPRESSION <expr> the expression to be evaluated returns the result of evaluating the expression (apply <fun> <args>) APPLY A FUNCTION TO A LIST OF ARGUMENTS <fun> the function to apply (or function symbol) <args> the argument list returns the result of applying the function to the argument list (funcall <fun> <arg>...) CALL A FUNCTION WITH ARGUMENTS <fun> the function to call (or function symbol) <arg> arguments to pass to the function returns the result of calling the function with the arguments (quote <expr>) RETURN AN EXPRESSION UNEVALUATED <expr> the expression to be quoted (quoted) returns <expr> unevaluated XLISP: An Experimental Object Oriented Language Page 14 SYMBOL FUNCTIONS 10.0 SYMBOL FUNCTIONS (set <sym> <expr>) SET THE VALUE OF A SYMBOL <sym> the symbol being set <expr> the new value returns the new value (setq <sym> <expr>) SET THE VALUE OF A SYMBOL <sym> the symbol being set (quoted) <expr> the new value returns the new value (defun <sym> <fargs> <expr>...) DEFINE A FUNCTION WITH EVALUATED ARGS (ndefun <sym> <fargs> <expr>...) DEFINE A FUNCTION WITH UNEVALUATED ARGS <sym> symbol being defined (quoted) <fargs> list of formal arguments (quoted) this list is of the form: (<farg>... [&rest <rarg>] [&aux <aux>...]) where <farg> is a formal argument <rarg> bound to the rest of the arguments <aux> is an auxiliary variable <expr> expressions constituting the body of the function (quoted) returns the function symbol (gensym <tag>) GENERATE A SYMBOL <tag> symbol/string/number returns the new symbol (intern <sym>) INTERN A SYMBOL ON THE OBLIST <sym> the symbol returns the interned symbol (symbol-name <sym>) GET THE PRINT NAME OF A SYMBOL <sym> the symbol returns the symbol's print name (symbol-plist <sym>) GET THE PROPERTY LIST OF A SYMBOL <sym> the symbol returns the symbol's property list XLISP: An Experimental Object Oriented Language Page 15 PROPERTY LIST FUNCTIONS 11.0 PROPERTY LIST FUNCTIONS (get <sym> <prop>) GET THE VALUE OF A PROPERTY <sym> the symbol <prop> the property symbol returns the property value or nil (putprop <sym> <value> <prop>) PUT A PROPERTY ONTO A PROPERTY LIST <sym> the symbol <value> the property value <prop> the property symbol returns the value (remprop <prop> <sym>) REMOVE A PROPERTY <sym> the symbol <prop> the property symbol returns nil XLISP: An Experimental Object Oriented Language Page 16 LIST FUNCTIONS 12.0 LIST FUNCTIONS (car <expr>) RETURN THE CAR OF A LIST NODE <expr> the list node returns the car of the list node (cdr <expr>) RETURN THE CDR OF A LIST NODE <expr> the list node returns the cdr of the list node (caar <expr>) == (car (car <expr>)) (cadr <expr>) == (car (cdr <expr>)) (cdar <expr>) == (cdr (car <expr>)) (cddr <expr>) == (cdr (cdr <expr>)) (cons <expr1> <expr2>) CONSTRUCT A NEW LIST NODE <expr1> the car of the new list node <expr2> the cdr of the new list node returns the new list node (list <expr>...) CREATE A LIST OF VALUES <expr> expressions to be combined into a list returns the new list (append <expr>...) APPEND LISTS <expr> lists whose elements are to be appended returns the new list (reverse <expr>) REVERSE A LIST <expr> the list to reverse returns a new list in the reverse order (last <list>) RETURN THE LAST LIST NODE OF A LIST <list> the list returns the last list node in the list (member <expr> <list>) FIND AN EXPRESSION IN A LIST <expr> the expression to find (equal test) <list> the list to search returns the remainder of the list starting with the expression (memq <expr> <list>) FIND AN EXPRESSION IN A LIST <expr> the expression to find (eq test) <list> the list to find it in returns the remainder of the list starting with the expression XLISP: An Experimental Object Oriented Language Page 17 LIST FUNCTIONS (assoc <expr> <alist>) FIND AN EXPRESSION IN AN ASSOCIATION LIST <expr> the expression to find (equal test) <alist> the association list returns the alist entry or nil (assq <expr> <alist>) FIND AN EXPRESSION IN AN ASSOCIATION LIST <expr> the expression to find (eq test) <alist> the association list returns the alist entry or nil (length <expr>) FIND THE LENGTH OF A LIST <expr> the list returns the length of the list (nth <n> <list>) RETURN THE NTH ELEMENT OF A LIST <n> the number of the element to return (zero origin) <list> the list returns the nth element or nil if the list isn't that long (nthcdr <n> <list>) RETURN THE NTH CDR OF A LIST <n> the number of the element to return (zero origin) <list> the list returns the nth cdr or nil if the list isn't that long (mapcar <fcn> <list1>...<listn>) APPLY FUNCTION TO SUCCESSIVE CARS <fcn> the function or function name <list1..n> a list for each argument of the function returns the list of values returned by each function invocation (maplist <fcn> <list1>...<listn>) APPLY FUNCTION TO SUCCESSIVE CDRS <fcn> the function or function name <list1..n> a list for each argument of the function returns the list of values returned by each function invocation (subst <to> <from> <expr>) SUBSTITUTE ONE EXPRESSION FOR ANOTHER <to> the new expression <from> the old expression <expr> the expression in which to do the substitutions returns the expression with substitutions (sublis <alist> <expr>) SUBSTITUTE USING AN ASSOCIATION LIST <alist> the association list <expr> the expression in which to do the substitutions returns the expression with substitutions XLISP: An Experimental Object Oriented Language Page 18 DESTRUCTIVE LIST FUNCTIONS 13.0 DESTRUCTIVE LIST FUNCTIONS (rplaca <list> <expr>) REPLACE THE CAR OF A LIST NODE <list> the list node <expr> the new value for the car of the list node returns the list node after updating the car (rplacd <list> <expr>) REPLACE THE CDR OF A LIST NODE <list> the list node <expr> the new value for the cdr of the list node returns the list node after updating the cdr (nconc <list>...) DESTRUCTIVELY CONCATENATE LISTS <list> lists to concatenate returns the result of concatenating the lists (delete <expr> <list>) DELETE OCCURANCES OF AN EXPRESSION FROM A LIST <expr> the expression to delete (equal test) <list> the list returns the list with the matching expressions deleted (delq <expr> <list>) DELETE OCCURANCES OF AN EXPRESSION FROM A LIST <expr> the expression to delete (eq test) <list> the list returns the list with the matching expressions deleted XLISP: An Experimental Object Oriented Language Page 19 PREDICATE FUNCTIONS 14.0 PREDICATE FUNCTIONS (atom <expr>) IS THIS AN ATOM? <expr> the expression to check returns t if the value is an atom, nil otherwise (symbolp <expr>) IS THIS A SYMBOL? <expr> the expression to check returns t if the expression is a symbol, nil otherwise (numberp <expr>) IS THIS A NUMBER? <expr> the expression to check returns t if the expression is a symbol, nil otherwise (null <expr>) IS THIS AN EMPTY LIST? <expr> the list to check returns t if the list is empty, nil otherwise (not <expr>) IS THIS FALSE? <expr> the expression to check return t if the expression is nil, nil otherwise (listp <expr>) IS THIS A LIST? <expr> the expression to check returns t if the value is a list node or nil, nil otherwise (consp <expr>) IS THIS A NON-EMPTY LIST? <expr> the expression to check returns t if the value is a list node, nil otherwise (boundp <sym>) IS THIS A BOUND SYMBOL? <sym> the symbol returns t if a value is bound to the symbol, nil otherwise (eq <expr1> <expr2>) ARE THE EXPRESSIONS IDENTICAL? <expr1> the first expression <expr2> the second expression returns t if they are equal, nil otherwise (equal <expr1> <expr2>) ARE THE EXPRESSIONS EQUAL? <expr1> the first expression <expr2> the second expression returns t if they are equal, nil otherwise XLISP: An Experimental Object Oriented Language Page 20 CONTROL FUNCTIONS 15.0 CONTROL FUNCTIONS (cond <pair>...) EVALUATE CONDITIONALLY <pair> pair consisting of: (<pred> <expr>...) where <pred> is a predicate expression <expr> evaluated if the predicate is not nil returns the value of the first expression whose predicate is not nil (let (<binding>...) <expr>...) BIND SYMBOLS AND EVALUATE EXPRESSIONS <binding> the variable bindings each of which is either: 1) a symbol (which is initialized to nil) 2) a list whose car is a symbol and whose cadr is an initialization expression <expr>... the expressions to be evaluated with the specified bindings returns the value of the last expression (and <expr>...) THE LOGICAL AND OF A LIST OF EXPRESSIONS <expr>... the expressions to be ANDed returns nil if any expression evaluates to nil, otherwise the value of the last expression (evaluation of expressions stops after the first expression that evaluates to nil) (or <expr>...) THE LOGICAL OR OF A LIST OF EXPRESSIONS <expr>... the expressions to be ORed returns nil if all expressions evaluate to nil, otherwise the value of the first non-nil expression (evaluation of expressions stops after the first expression that does not evaluate to nil) (if <texpr> <expr1> [<expr2>]) EXECUTE EXPRESSIONS CONDITIONALLY <texpr> the test expression <expr1> the expression to be evaluated if texpr is non-nil <expr2> the expression to be evaluated if texpr is nil returns the value of the selected expression (progn <expr>...) EXECUTE EXPRESSIONS SEQUENTIALLY <expr>... the expressions to evaluate returns the value of the last expression (while <texpr> <expr>...) ITERATE WHILE AN EXPRESSION IS TRUE <texpr> the test expression evaluated at start of each iteration <expr>... the expressions evaluated as long as <texpr> evaluates to non-nil returns the value of the last expression XLISP: An Experimental Object Oriented Language Page 21 CONTROL FUNCTIONS (repeat <iexpr> <expr>...) ITERATE USING A REPEAT COUNT <iexpr> the integer expression indicating the repeat count <expr>... the expressions evaluated <iexpr> times returns the value of the last expression XLISP: An Experimental Object Oriented Language Page 22 ARITHMETIC FUNCTIONS 16.0 ARITHMETIC FUNCTIONS (+ <expr>...) ADD A LIST OF NUMBERS <expr>... the numbers returns the result of the addition (- <expr>...) SUBTRACT A LIST OF NUMBERS <expr>... the numbers returns the result of the subtraction (* <expr>...) MULTIPLY A LIST OF NUMBERS <expr>... the numbers returns the result of the multiplication (/ <expr>...) DIVIDE A LIST OF NUMBERS <expr>... the numbers returns the result of the division (1+ <expr>) ADD ONE TO A NUMBER <expr> the number returns the number plus one (1- <expr>) SUBTRACT ONE FROM A NUMBER <expr> the number returns the number minus one (rem <expr>...) REMAINDER OF A LIST OF NUMBERS <expr>... the numbers returns the result of the remainder operation (minus <expr>) NEGATE A NUMBER <expr> the number returns the number negated (min <expr>...) THE SMALLEST OF A LIST OF NUMBERS <expr>... the expressions to be checked returns the smallest number in the list (max <expr>...) THE LARGEST OF A LIST OF NUMBERS <expr>... the expressions to be checked returns the largest number in the list (abs <expr>) THE ABSOLUTE VALUE OF A NUMBER <expr> the number returns the absolute value of the number XLISP: An Experimental Object Oriented Language Page 23 BITWISE LOGICAL FUNCTIONS 17.0 BITWISE LOGICAL FUNCTIONS (bit-and <expr>...) THE BITWISE AND OF A LIST OF NUMBERS <expr> the numbers returns the result of the and operation (bit-ior <expr...) THE BITWISE INCLUSIVE OR OF A LIST OF NUMBERS <expr> the numbers returns the result of the inclusive or operation (bit-xor <expr...) THE BITWISE EXCLUSIVE OR OF A LIST OF NUMBERS <expr> the numbers returns the result of the exclusive or operation (bit-not <expr>) THE BITWISE NOT OF A NUMBER <expr> the number returns the bitwise inversion of number XLISP: An Experimental Object Oriented Language Page 24 RELATIONAL FUNCTIONS 18.0 RELATIONAL FUNCTIONS The relational functions can be used to compare integers or strings. The functions '=' and '/=' can also be used to compare other types. The result of these comparisons is computed the same way as for 'eq'. (< <e1> <e2>) TEST FOR LESS THAN <e1> the left operand of the comparison <e2> the right operand of the comparison returns the result of comparing <e1> with <e2> (<= <e1> <e2>) TEST FOR LESS THAN OR EQUAL TO <e1> the left operand of the comparison <e2> the right operand of the comparison returns the result of comparing <e1> with <e2> (= <e1> <e2>) TEST FOR EQUAL TO <e1> the left operand of the comparison <e2> the right operand of the comparison returns the result of comparing <e1> with <e2> (/= <e1> <e2>) TEST FOR NOT EQUAL TO <e1> the left operand of the comparison <e2> the right operand of the comparison returns the result of comparing <e1> with <e2> (>= <e1> <e2>) TEST FOR GREATER THAN OR EQUAL TO <e1> the left operand of the comparison <e2> the right operand of the comparison returns the result of comparing <e1> with <e2> (> <e1> <e2>) TEST FOR GREATER THAN <e1> the left operand of the comparison <e2> the right operand of the comparison returns the result of comparing <e1> with <e2> XLISP: An Experimental Object Oriented Language Page 25 STRING FUNCTIONS 19.0 STRING FUNCTIONS (strcat <expr>...) CONCATENATE STRINGS <expr>... the strings to concatenate returns the result of concatenating the strings (strlen <expr>) COMPUTE THE LENGTH OF A STRING <expr> the string returns the length of the string (substr <expr> <sexpr> [<lexpr>]) EXTRACT A SUBSTRING <expr> the string <sexpr> the starting position <lexpr> the length (default is rest of string) returns substring starting at <sexpr> for <lexpr> (ascii <expr>) NUMERIC VALUE OF CHARACTER <expr> the string returns the ascii code of the first character (chr <expr>) CHARACTER EQUIVALENT OF ASCII VALUE <expr> the numeric expression returns a one character string whose first character is <expr> (atoi <expr>) CONVERT AN ASCII STRING TO AN INTEGER <expr> the string returns the integer value of the string expression (itoa <expr>) CONVERT AN INTEGER TO AN ASCII STRING <expr> the integer returns the string representation of the integer value XLISP: An Experimental Object Oriented Language Page 26 INPUT/OUTPUT FUNCTIONS 20.0 INPUT/OUTPUT FUNCTIONS (read [<source>[<eof>]]) READ AN XLISP EXPRESSION <source> the input source (default is standard input) <eof> the value to return on end of file (default is nil) returns the expression read (print <expr> [<sink>]) PRINT A LIST OF VALUES ON A NEW LINE <expr> the expressions to be printed <sink> the output sink (default is standard output) returns nil (prin1 <expr> [<sink>]) PRINT A LIST OF VALUES <expr> the expressions to be printed <sink> the output sink (default is standard output) returns nil (princ <expr> [<sink>]) PRINT A LIST OF VALUES WITHOUT QUOTING <expr> the expressions to be printed <sink> the output sink (default is standard output) returns nil (terpri [<sink>]) TERMINATE THE CURRENT PRINT LINE <sink> the output sink (default is standard output) returns nil (flatsize <expr>) LENGTH OF PRINTED REPRESENTATION USING PRIN1 <expr> the expression returns the length (flatc <expr>) LENGTH OF PRINTED REPRESENTATION USING PRINC <expr> the expression returns the length (explode <expr>) CHARACTERS IN PRINTED REPRESENTATION USING PRIN1 <expr> the expression returns the list of characters (explodec <expr>) CHARACTERS IN PRINTED REPRESENTATION USING PRINC <expr> the expression returns the list of characters (maknam <list>) BUILD AN UNINTERNED SYMBOL FROM A LIST OF CHARACTERS <list> list of characters in symbol name returns the symbol (implode <list>) BUILD AN INTERNED SYMBOL FROM A LIST OF CHARACTERS <list> list of characters in symbol name returns the symbol XLISP: An Experimental Object Oriented Language Page 27 FILE I/O FUNCTIONS 21.0 FILE I/O FUNCTIONS (openi <fname>) OPEN AN INPUT FILE <fname> the file name string returns a file pointer (openo <fname>) OPEN AN OUTPUT FILE <fname> the file name string returns a file pointer (close <fp>) CLOSE A FILE <fp> the file pointer returns nil (read-char [<source>]) READ A CHARACTER FROM A FILE OR STREAM <source> the input source (default is standard input) returns the character (integer) (peek-char [<flag> [<source>]]) PEEK AT THE NEXT CHARACTER <flag> flag for skipping white space (default is nil) <source> the input source (default is standard input) returns the character (integer) (write-char <ch> [<sink>]) WRITE A CHARACTER TO A FILE OR STREAM <ch> the character to put (integer) <sink> the output sink (default is standard output) returns the character (integer) (readline [<source>]) READ A LINE FROM A FILE OR STREAM <source> the input source (default is standard input) returns the input string XLISP: An Experimental Object Oriented Language Page 28 SYSTEM FUNCTIONS 22.0 SYSTEM FUNCTIONS (load <fname>) LOAD AN XLISP SOURCE FILE <fname> the filename string (".lsp" is appended) returns the filename (gc) FORCE GARBAGE COLLECTION returns nil (expand <num>) EXPAND MEMORY BY ADDING SEGMENTS <num> the number of segments to add returns the number of segments added (alloc <num>) CHANGE NUMBER OF NODES TO ALLOCATE IN EACH SEGMENT <num> the number of nodes to allocate returns the old number of nodes to allocate (mem) SHOW MEMORY ALLOCATION STATISTICS returns nil (type <expr>) RETURNS THE TYPE OF THE EXPRESSION <expr> the expression to return the type of returns nil if the value is nil otherwise one of the symbols: SYM for symbols OBJ for objects LIST for list nodes SUBR for subroutine nodes with evaluated arguments FSUBR for subroutine nodes with unevaluated arguments STR for string nodes INT for integer nodes FPTR for file pointer nodes (exit) EXIT XLISP returns never returns d returns the number of segments added (