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Text File | 1995-07-26 | 18.7 KB | 390 lines

eeeexxxxpppprrrr((((nnnn)))) TTTTccccllll ((((7777....0000)))) eeeexxxxpppprrrr((((nnnn)))) _________________________________________________________________ NNNNAAAAMMMMEEEE expr - Evalue an expression SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS eeeexxxxpppprrrr _a_r_g ?_a_r_g _a_r_g ...? _________________________________________________________________ DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN Concatenates _a_r_g's (adding separator spaces between them), | evaluates the result as a Tcl expression, and returns the | value. The operators permitted in Tcl expressions are a subset of the operators permitted in C expressions, and they have the same meaning and precedence as the corresponding C operators. Expressions almost always yield numeric results (integer or floating-point values). For example, the expression eeeexxxxpppprrrr 8888....2222 ++++ 6666 evaluates to 14.2. Tcl expressions differ from C expressions in the way that operands are specified. Also, Tcl expressions support non-numeric operands and string comparisons. OOOOPPPPEEEERRRRAAAANNNNDDDDSSSS A Tcl expression consists of a combination of operands, operators, and parentheses. White space may be used between the operands and operators and parentheses; it is ignored by the expression processor. Where possible, operands are interpreted as integer values. Integer values may be specified in decimal (the normal case), in octal (if the first character of the operand is 0000), or in hexadecimal (if the first two characters of the operand are 0000xxxx). If an operand does not have one of the integer formats given above, then it is treated as a floating-point number if that is possible. Floating-point numbers may be specified in any of the ways accepted by an ANSI-compliant C compiler (except that the ``f'', ``F'', ``l'', and ``L'' suffixes will not be permitted in most installations). For example, all of the following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16. If no numeric interpretation is possible, then an operand is left as a string (and only a limited set of operators may be applied to it). Operands may be specified in any of the following ways: [1] As an numeric value, either integer or floating-point. [2] As a Tcl variable, using standard $$$$ notation. The variable's value will be used as the operand. Page 1 (printed 7/17/95) eeeexxxxpppprrrr((((nnnn)))) TTTTccccllll ((((7777....0000)))) eeeexxxxpppprrrr((((nnnn)))) [3] As a string enclosed in double-quotes. The expression parser will perform backslash, variable, and command substitutions on the information between the quotes, and use the resulting value as the operand [4] As a string enclosed in braces. The characters between the open brace and matching close brace will be used as the operand without any substitutions. [5] As a Tcl command enclosed in brackets. The command will be executed and its result will be used as the operand. [6] As a mathematical function whose arguments have any of | the above forms for operands, such as ``ssssiiiinnnn(((($$$$xxxx))))''. See | below for a list of defined functions. Where substitutions occur above (e.g. inside quoted strings), they are performed by the expression processor. However, an additional layer of substitution may already have been performed by the command parser before the expression processor was called. As discussed below, it is usually best to enclose expressions in braces to prevent the command parser from performing substitutions on the contents. For some examples of simple expressions, suppose the variable aaaa has the value 3 and the variable bbbb has the value 6. Then the command on the left side of each of the lines below will produce the value on the right side of the line: eeeexxxxpppprrrr 3333....1111 ++++ $$$$aaaa 6666....1111 eeeexxxxpppprrrr 2222 ++++ """"$$$$aaaa....$$$$bbbb"""" 5555....6666 eeeexxxxpppprrrr 4444****[[[[lllllllleeeennnnggggtttthhhh """"6666 2222""""]]]] 8888 eeeexxxxpppprrrr {{{{{{{{wwwwoooorrrrdddd oooonnnneeee}}}} <<<< """"wwwwoooorrrrdddd $$$$aaaa""""}}}}0000 OOOOPPPPEEEERRRRAAAATTTTOOOORRRRSSSS The valid operators are listed below, grouped in decreasing order of precedence: ---- ~~~~ !!!! Unary minus, bit-wise NOT, logical NOT. None of these operands may be applied to string operands, and bit-wise NOT may be applied only to integers. **** //// %%%% Multiply, divide, remainder. None of these operands may be applied to string operands, and remainder may be applied only to integers. The remainder will | always have the same sign as the divisor | and an absolute value smaller than the | divisor. Page 2 (printed 7/17/95) eeeexxxxpppprrrr((((nnnn)))) TTTTccccllll ((((7777....0000)))) eeeexxxxpppprrrr((((nnnn)))) ++++ ---- Add and subtract. Valid for any numeric operands. <<<<<<<< >>>>>>>> Left and right shift. Valid for integer operands only. <<<< >>>> <<<<==== >>>>==== Boolean less, greater, less than or equal, and greater than or equal. Each operator produces 1 if the condition is true, 0 otherwise. These operators may be applied to strings as well as numeric operands, in which case string comparison is used. ======== !!!!==== Boolean equal and not equal. Each operator produces a zero/one result. Valid for all operand types. &&&& Bit-wise AND. Valid for integer operands only. ^^^^ Bit-wise exclusive OR. Valid for integer operands only. |||| Bit-wise OR. Valid for integer operands only. &&&&&&&& Logical AND. Produces a 1 result if both operands are non-zero, 0 otherwise. Valid for numeric operands only (integers or floating-point). |||||||| Logical OR. Produces a 0 result if both operands are zero, 1 otherwise. Valid for numeric operands only (integers or floating-point). _x????_y::::_z If-then-else, as in C. If _x evaluates to non-zero, then the result is the value of _y. Otherwise the result is the value of _z. The _x operand must have a numeric value. See the C manual for more details on the results produced by each operator. All of the binary operators group left-to- right within the same precedence level. For example, the command eeeexxxxpppprrrr 4444****2222 <<<< 7777 returns 0. Page 3 (printed 7/17/95) eeeexxxxpppprrrr((((nnnn)))) TTTTccccllll ((((7777....0000)))) eeeexxxxpppprrrr((((nnnn)))) The &&&&&&&&, ||||||||, and ????:::: operators have ``lazy evaluation'', just as in C, which means that operands are not evaluated if they are not needed to determine the outcome. For example, in the command eeeexxxxpppprrrr {{{{$$$$vvvv ???? [[[[aaaa]]]] :::: [[[[bbbb]]]]}}}} only one of [[[[aaaa]]]] or [[[[bbbb]]]] will actually be evaluated, depending on the value of $$$$vvvv. Note, however, that this is only true if the entire expression is enclosed in braces; otherwise the Tcl parser will evaluate both [[[[aaaa]]]] and [[[[bbbb]]]] before invoking the eeeexxxxpppprrrr command. MMMMAAAATTTTHHHH FFFFUUUUNNNNCCCCTTTTIIIIOOOONNNNSSSS Tcl supports the following mathematical functions in | expressions: | aaaaccccoooossss ccccoooossss hhhhyyyyppppooootttt ssssiiiinnnnhhhh | aaaassssiiiinnnn ccccoooosssshhhh lllloooogggg ssssqqqqrrrrtttt | aaaattttaaaannnn eeeexxxxpppp lllloooogggg11110000 ttttaaaannnn | aaaattttaaaannnn2222 fffflllloooooooorrrr ppppoooowwww ttttaaaannnnhhhh | cccceeeeiiiillll ffffmmmmoooodddd ssssiiiinnnn | Each of these functions invokes the math library function of | the same name; see the manual entries for the library | functions for details on what they do. Tcl also implements | the following functions for conversion between integers and | floating-point numbers: | aaaabbbbssss((((_a_r_g)))) || Returns the absolute value of _a_r_g. _A_r_g may be either | integer or floating-point, and the result is returned | in the same form. | ddddoooouuuubbbblllleeee((((_a_r_g)))) || If _a_r_g is a floating value, returns _a_r_g, otherwise | converts _a_r_g to floating and returns the converted | value. | iiiinnnntttt((((_a_r_g)))) || If _a_r_g is an integer value, returns _a_r_g, otherwise | converts _a_r_g to integer by truncation and returns the | converted value. | rrrroooouuuunnnndddd((((_a_r_g)))) || If _a_r_g is an integer value, returns _a_r_g, otherwise | converts _a_r_g to integer by rounding and returns the | converted value. | In addition to these predifined functions, applications may | define additional functions using TTTTccccllll____CCCCrrrreeeeaaaatttteeeeMMMMaaaatttthhhhFFFFuuuunnnncccc(). TTTTYYYYPPPPEEEESSSS,,,, OOOOVVVVEEEERRRRFFFFLLLLOOOOWWWW,,,, AAAANNNNDDDD PPPPRRRREEEECCCCIIIISSSSIIIIOOOONNNN PPPPaaaaggggeeee 4444 ((((pppprrrriiiinnnntttteeeedddd 7777////11117777////99995555)))) eeeexxxxpppprrrr((((nnnn)))) TTTTccccllll ((((7777....0000)))) eeeexxxxpppprrrr((((nnnn)))) All internal computations involving integers are done with the C type _l_o_n_g, and all internal computations involving floating-point are done with the C type _d_o_u_b_l_e. When converting a string to floating-point, exponent overflow is detected and results in a Tcl error. For conversion to integer from string, detection of overflow depends on the behavior of some routines in the local C library, so it should be regarded as unreliable. In any case, integer overflow and underflow are generally not detected reliably for intermediate results. Floating-point overflow and underflow are detected to the degree supported by the hardware, which is generally pretty reliable. Conversion among internal representations for integer, floating-point, and string operands is done automatically as needed. For arithmetic computations, integers are used until some floating-point number is introduced, after which floating-point is used. For example, eeeexxxxpppprrrr 5555 //// 4444 returns 1, while eeeexxxxpppprrrr 5555 //// 4444....0000 eeeexxxxpppprrrr 5555 //// (((( [[[[ssssttttrrrriiiinnnngggg lllleeeennnnggggtttthhhh """"aaaabbbbccccdddd""""]]]] ++++ 0000....0000 )))) both return 1.25. Floating-point values are always returned | with a ``.'' or an ``e'' so that they will not look like | integer values. For example, | eeeexxxxpppprrrr 22220000....0000////5555....0000 | returns ``4.0'', not ``4''. The global variable | ttttccccllll____pppprrrreeeecccciiiissssiiiioooonnnn determines the the number of significant | digits that are retained when floating values are converted | to strings (except that trailing zeroes are omitted). If | ttttccccllll____pppprrrreeeecccciiiissssiiiioooonnnn is unset then 6 digits of precision are used. | To retain all of the significant bits of an IEEE floating- | point number set ttttccccllll____pppprrrreeeecccciiiissssiiiioooonnnn to 17; if a value is | converted to string with 17 digits of precision and then | converted back to binary for some later calculation, the | resulting binary value is guaranteed to be identical to the | original one. SSSSTTTTRRRRIIIINNNNGGGG OOOOPPPPEEEERRRRAAAATTTTIIIIOOOONNNNSSSS String values may be used as operands of the comparison operators, although the expression evaluator tries to do comparisons as integer or floating-point when it can. If one of the operands of a comparison is a string and the other has a numeric value, the numeric operand is converted back to a string using the C _s_p_r_i_n_t_f format specifier %%%%dddd for integers and %%%%gggg for floating-point values. For example, the commands Page 5 (printed 7/17/95) eeeexxxxpppprrrr((((nnnn)))) TTTTccccllll ((((7777....0000)))) eeeexxxxpppprrrr((((nnnn)))) eeeexxxxpppprrrr {{{{""""0000xxxx00003333"""" >>>> """"2222""""}}}} eeeexxxxpppprrrr {{{{""""0000yyyy"""" <<<< """"0000xxxx11112222""""}}}} both return 1. The first comparison is done using integer comparison, and the second is done using string comparison after the second operand is converted to the string ``18''. KKKKEEEEYYYYWWWWOOOORRRRDDDDSSSS arithmetic, boolean, compare, expression Page 6 (printed 7/17/95)