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Diffstat (limited to 'doc/expr.n')
| -rw-r--r-- | doc/expr.n | 105 |
1 files changed, 83 insertions, 22 deletions
@@ -6,10 +6,8 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: expr.n,v 1.35 2008/06/29 22:28:24 dkf Exp $ -'\" -.so man.macros .TH expr n 8.5 Tcl "Tcl Built-In Commands" +.so man.macros .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME @@ -28,9 +26,11 @@ as the corresponding C operators. Expressions almost always yield numeric results (integer or floating-point values). For example, the expression +.PP .CS -\fBexpr 8.2 + 6\fR +\fBexpr\fR 8.2 + 6 .CE +.PP evaluates to 14.2. Tcl expressions differ from C expressions in the way that operands are specified. Also, Tcl expressions support @@ -39,9 +39,9 @@ additional operators not found in C. .SS OPERANDS .PP A Tcl expression consists of a combination of operands, operators, -and parentheses. +parentheses and commas. White space may be used between the operands and operators and -parentheses; it is ignored by the expression's instructions. +parentheses (or commas); it is ignored by the expression's instructions. Where possible, operands are interpreted as integer values. Integer values may be specified in decimal (the normal case), in binary (if the first two characters of the operand are \fB0b\fR), in octal @@ -68,7 +68,8 @@ Operands may be specified in any of the following ways: .IP [1] As a numeric value, either integer or floating-point. .IP [2] -As a boolean value, using any form understood by \fBstring is boolean\fR. +As a boolean value, using any form understood by \fBstring is\fR +\fBboolean\fR. .IP [3] As a Tcl variable, using standard \fB$\fR notation. The variable's value will be used as the operand. @@ -103,6 +104,7 @@ For some examples of simple expressions, suppose the variable the variable \fBb\fR 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: +.PP .CS .ta 6c \fBexpr\fR 3.1 + $a \fI6.1\fR @@ -132,7 +134,20 @@ Multiply, divide, remainder. None of these operators may be applied to string operands, and remainder may be applied only to integers. The remainder will always have the same sign as the divisor and -an absolute value smaller than the divisor. +an absolute value smaller than the absolute value of the divisor. +.RS +.PP +When applied to integers, the division and remainder operators can be +considered to partition the number line into a sequence of equal-sized +adjacent non-overlapping pieces where each piece is the size of the divisor; +the division result identifies which piece the divisor lay within, and the +remainder result identifies where within that piece the divisor lay. A +consequence of this is that the result of +.QW "-57 \fB/\fR 10" +is always -6, and the result of +.QW "-57 \fB%\fR 10" +is always 3. +.RE .TP 20 \fB+\0\0\-\fR . @@ -203,20 +218,30 @@ produced by each operator. The exponentiation operator promotes types like the multiply and divide operators, and produces a result that is the same as the output of the \fBpow\fR function (after any type conversions.) -All of the binary operators group left-to-right within the same -precedence level. For example, the command +All of the binary operators but exponentiation group left-to-right +within the same precedence level; exponentiation groups right-to-left. For example, the command +.PP .CS \fBexpr\fR {4*2 < 7} .CE -returns 0. +.PP +returns 0, while +.PP +.CS +\fBexpr\fR {2**3**2} +.CE +.PP +returns 512. .PP The \fB&&\fR, \fB||\fR, and \fB?:\fR operators have .QW "lazy evaluation" , just as in C, which means that operands are not evaluated if they are not needed to determine the outcome. For example, in the command +.PP .CS -\fBexpr {$v ? [a] : [b]}\fR +\fBexpr\fR {$v ? [a] : [b]} .CE +.PP only one of .QW \fB[a]\fR or @@ -235,16 +260,21 @@ When the expression parser encounters a mathematical function such as \fBsin($x)\fR, it replaces it with a call to an ordinary Tcl function in the \fBtcl::mathfunc\fR namespace. The processing of an expression such as: +.PP .CS -\fBexpr {sin($x+$y)}\fR +\fBexpr\fR {sin($x+$y)} .CE +.PP is the same in every way as the processing of: +.PP .CS -\fBexpr {[tcl::mathfunc::sin [expr {$x+$y}]]}\fR +\fBexpr\fR {[tcl::mathfunc::sin [\fBexpr\fR {$x+$y}]]} .CE +.PP which in turn is the same as the processing of: +.PP .CS -\fBtcl::mathfunc::sin [expr {$x+$y}]\fR +tcl::mathfunc::sin [\fBexpr\fR {$x+$y}] .CE .PP The executor will search for \fBtcl::mathfunc::sin\fR using the usual @@ -253,6 +283,18 @@ rules for resolving functions in namespaces. Either current]::tcl::mathfunc::sin\fR will satisfy the request, and others may as well (depending on the current \fBnamespace path\fR setting). .PP +Some mathematical functions have several arguments, separated by commas like in C. Thus: +.PP +.CS +\fBexpr\fR {hypot($x,$y)} +.CE +.PP +ends up as +.PP +.CS +tcl::mathfunc::hypot $x $y +.CE +.PP See the \fBmathfunc\fR(n) manual page for the math functions that are available by default. .SS "TYPES, OVERFLOW, AND PRECISION" @@ -280,29 +322,36 @@ 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, +.PP .CS \fBexpr\fR {5 / 4} .CE +.PP returns 1, while +.PP .CS \fBexpr\fR {5 / 4.0} \fBexpr\fR {5 / ( [string length "abcd"] + 0.0 )} .CE +.PP both return 1.25. Floating-point values are always returned with a .QW \fB.\fR or an .QW \fBe\fR so that they will not look like integer values. For example, +.PP .CS \fBexpr\fR {20.0/5.0} .CE +.PP returns \fB4.0\fR, not \fB4\fR. .SS "STRING OPERATIONS" .PP 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, +i.e., when all arguments to the operator allow numeric interpretations, except in the case of the \fBeq\fR and \fBne\fR operators. If one of the operands of a comparison is a string and the other has a numeric value, a canonical string representation of the numeric @@ -311,13 +360,14 @@ Canonical string representation for integer values is a decimal string format. Canonical string representation for floating-point values is that produced by the \fB%g\fR format specifier of Tcl's \fBformat\fR command. For example, the commands +.PP .CS -\fBexpr {"0x03" > "2"}\fR -\fBexpr {"0y" < "0x12"}\fR +\fBexpr\fR {"0x03" > "2"} +\fBexpr\fR {"0y" > "0x12"} .CE +.PP 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 \fB18\fR. +comparison, and the second is done using string comparison. Because of Tcl's tendency to treat values as numbers whenever possible, it is not generally a good idea to use operators like \fB==\fR when you really want string comparison and the values of the @@ -332,11 +382,13 @@ This allows the Tcl bytecode compiler to generate the best code. As mentioned above, expressions are substituted twice: once by the Tcl parser and once by the \fBexpr\fR command. For example, the commands +.PP .CS -\fBset a 3\fR -\fBset b {$a + 2}\fR -\fBexpr $b*4\fR +set a 3 +set b {$a + 2} +\fBexpr\fR $b*4 .CE +.PP return 11, not a multiple of 4. This is because the Tcl parser will first substitute \fB$a + 2\fR for the variable \fBb\fR, @@ -362,6 +414,7 @@ operator, consider using the commands documented in the \fBmathfunc\fR(n) or Define a procedure that computes an .QW interesting mathematical function: +.PP .CS proc tcl::mathfunc::calc {x y} { \fBexpr\fR { ($x**2 - $y**2) / exp($x**2 + $y**2) } @@ -369,6 +422,7 @@ proc tcl::mathfunc::calc {x y} { .CE .PP Convert polar coordinates into cartesian coordinates: +.PP .CS # convert from ($radius,$angle) set x [\fBexpr\fR { $radius * cos($angle) }] @@ -376,6 +430,7 @@ set y [\fBexpr\fR { $radius * sin($angle) }] .CE .PP Convert cartesian coordinates into polar coordinates: +.PP .CS # convert from ($x,$y) set radius [\fBexpr\fR { hypot($y, $x) }] @@ -384,12 +439,14 @@ set angle [\fBexpr\fR { atan2($y, $x) }] .PP Print a message describing the relationship of two string values to each other: +.PP .CS puts "a and b are [\fBexpr\fR {$a eq $b ? {equal} : {different}}]" .CE .PP Set a variable to whether an environment variable is both defined at all and also set to a true boolean value: +.PP .CS set isTrue [\fBexpr\fR { [info exists ::env(SOME_ENV_VAR)] && @@ -398,6 +455,7 @@ set isTrue [\fBexpr\fR { .CE .PP Generate a random integer in the range 0..99 inclusive: +.PP .CS set randNum [\fBexpr\fR { int(100 * rand()) }] .CE @@ -412,3 +470,6 @@ Copyright (c) 1993 The Regents of the University of California. Copyright (c) 1994-2000 Sun Microsystems Incorporated. Copyright (c) 2005 by Kevin B. Kenny <kennykb@acm.org>. All rights reserved. .fi +'\" Local Variables: +'\" mode: nroff +'\" End: |