diff options
Diffstat (limited to 'doc/expr.n')
| -rw-r--r-- | doc/expr.n | 29 |
1 files changed, 28 insertions, 1 deletions
@@ -6,7 +6,7 @@ '\" 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 $ +'\" RCS: @(#) $Id: expr.n,v 1.36 2008/10/15 10:43:37 dkf Exp $ '\" .so man.macros .TH expr n 8.5 Tcl "Tcl Built-In Commands" @@ -28,9 +28,11 @@ 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 .CE +.PP evaluates to 14.2. Tcl expressions differ from C expressions in the way that operands are specified. Also, Tcl expressions support @@ -205,18 +207,22 @@ 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 +.PP .CS \fBexpr\fR {4*2 < 7} .CE +.PP returns 0. .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 {$v ? [a] : [b]}\fR .CE +.PP only one of .QW \fB[a]\fR or @@ -235,14 +241,19 @@ When the expression parser encounters a mathematical function such as \fBsin($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 .CE +.PP is the same in every way as the processing of: +.PP .CS \fBexpr {[tcl::mathfunc::sin [expr {$x+$y}]]}\fR .CE +.PP which in turn is the same as the processing of: +.PP .CS \fBtcl::mathfunc::sin [expr {$x+$y}]\fR .CE @@ -280,23 +291,29 @@ 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 @@ -311,10 +328,12 @@ 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 .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. @@ -332,11 +351,13 @@ 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 $b*4\fR .CE +.PP return 11, not a multiple of 4. This is because the Tcl parser will first substitute \fB$a + 2\fR for the variable \fBb\fR, @@ -362,6 +383,7 @@ 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 + $y**2) } @@ -369,6 +391,7 @@ proc tcl::mathfunc::calc {x y} { .CE .PP Convert polar coordinates into cartesian coordinates: +.PP .CS # convert from ($radius,$angle) set x [\fBexpr\fR { $radius * cos($angle) }] @@ -376,6 +399,7 @@ 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, $x) }] @@ -384,12 +408,14 @@ set angle [\fBexpr\fR { atan2($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 +424,7 @@ 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 |