diff options
Diffstat (limited to 'doc/expr.n')
| -rw-r--r-- | doc/expr.n | 116 |
1 files changed, 84 insertions, 32 deletions
@@ -26,9 +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 @@ -37,11 +39,10 @@ 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. -.VS 8.5 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 (if the first two characters of the operand are \fB0o\fR), or in hexadecimal @@ -58,7 +59,6 @@ the sign characters \fB+\fR or \fB\-\fR. For example, all of the following are valid floating-point numbers: 2.1, 3., 6e4, 7.91e+16. Also recognized as floating point values are the strings \fBInf\fR and \fBNaN\fR making use of any case for each character. -.VE 8.5 If no numeric interpretation is possible (note that all literal operands that are not numeric or boolean must be quoted with either braces or with double quotes), then an operand is left as a string @@ -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$\fR notation. The variable's value will be used as the operand. @@ -89,7 +90,7 @@ the operand. As a mathematical function whose arguments have any of the above forms for operands, such as \fBsin($x)\fR. See \fBMATH FUNCTIONS\fR below for a discussion of how mathematical functions are handled. -.LP +.PP Where the above substitutions occur (e.g. inside quoted strings), they are performed by the expression's instructions. However, the command parser may already have performed one round of @@ -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 @@ -117,16 +119,17 @@ the \fBtcl::mathop\fR namespace; see the \fBmathop\fR(n) manual page for details) are listed below, grouped in decreasing order of precedence: .TP 20 \fB\-\0\0+\0\0~\0\0!\fR +. Unary minus, unary plus, bit-wise NOT, logical NOT. None of these operators may be applied to string operands, and bit-wise NOT may be applied only to integers. .TP 20 \fB**\fR -.VS 8.5 +. Exponentiation. Valid for any numeric operands. -.VE 8.5 .TP 20 \fB*\0\0/\0\0%\fR +. Multiply, divide, remainder. None of these operators may be applied to string operands, and remainder may be applied only to integers. @@ -147,80 +150,98 @@ is always 3. .RE .TP 20 \fB+\0\0\-\fR +. Add and subtract. Valid for any numeric operands. .TP 20 \fB<<\0\0>>\fR +. Left and right shift. Valid for integer operands only. A right shift always propagates the sign bit. .TP 20 \fB<\0\0>\0\0<=\0\0>=\fR +. 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. .TP 20 \fB==\0\0!=\fR +. Boolean equal and not equal. Each operator produces a zero/one result. Valid for all operand types. .TP 20 \fBeq\0\0ne\fR +. Boolean string equal and string not equal. Each operator produces a zero/one result. The operand types are interpreted only as strings. .TP 20 \fBin\0\0ni\fR -.VS 8.5 +. List containment and negated list containment. Each operator produces a zero/one result and treats its first argument as a string and its second argument as a Tcl list. The \fBin\fR operator indicates whether the first argument is a member of the second argument list; the \fBni\fR operator inverts the sense of the result. -.VE 8.5 .TP 20 \fB&\fR +. Bit-wise AND. Valid for integer operands only. .TP 20 \fB^\fR +. Bit-wise exclusive OR. Valid for integer operands only. .TP 20 \fB|\fR +. Bit-wise OR. Valid for integer operands only. .TP 20 \fB&&\fR +. Logical AND. Produces a 1 result if both operands are non-zero, 0 otherwise. Valid for boolean and numeric (integers or floating-point) operands only. .TP 20 \fB||\fR +. Logical OR. Produces a 0 result if both operands are zero, 1 otherwise. Valid for boolean and numeric (integers or floating-point) operands only. .TP 20 \fIx\fB?\fIy\fB:\fIz\fR +. If-then-else, as in C. If \fIx\fR evaluates to non-zero, then the result is the value of \fIy\fR. Otherwise the result is the value of \fIz\fR. The \fIx\fR operand must have a boolean or numeric value. -.LP +.PP See the C manual for more details on the results produced by each operator. -.VS 8.5 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.) -.VE 8.5 -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 {$v ? [a] : [b]} .CE +.PP only one of .QW \fB[a]\fR or @@ -235,21 +256,25 @@ and before invoking the \fBexpr\fR command. .SS "MATH FUNCTIONS" .PP -.VS 8.5 When the expression parser encounters a mathematical function such as \fBsin($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 @@ -258,12 +283,22 @@ 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. -.VE 8.5 .SS "TYPES, OVERFLOW, AND PRECISION" .PP -.VS 8.5 All internal computations involving integers are done calling on the LibTomMath multiple precision integer library as required so that all integer calculations are performed exactly. Note that in Tcl releases @@ -273,7 +308,6 @@ in those calculations where values overflowed the range of those types. Any code that relied on these implicit truncations will need to explicitly add \fBint()\fR or \fBwide()\fR function calls to expressions at the points where such truncation is required to take place. -.VE 8.5 .PP All internal computations involving floating-point are done with the C type \fIdouble\fR. @@ -288,23 +322,29 @@ 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 @@ -320,10 +360,12 @@ 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 +\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. Because of Tcl's tendency to treat values as numbers whenever @@ -340,11 +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, @@ -362,15 +406,15 @@ The most expensive code is required for unbraced expressions that contain command substitutions. These expressions must be implemented by generating new code each time the expression is executed. -.VS 8.5 When the expression is unbraced to allow the substitution of a function or operator, consider using the commands documented in the \fBmathfunc\fR(n) or \fBmathop\fR(n) manual pages directly instead. -.VE 8.5 .SH EXAMPLES +.PP 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 + $y**2) } @@ -378,6 +422,7 @@ proc tcl::mathfunc::calc {x y} { .CE .PP Convert polar coordinates into cartesian coordinates: +.PP .CS # convert from ($radius,$angle) set x [\fBexpr\fR { $radius * cos($angle) }] @@ -385,6 +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, $x) }] @@ -393,12 +439,14 @@ set angle [\fBexpr\fR { atan2($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)] && @@ -407,6 +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 @@ -421,3 +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: |