Programmer Guide/Command Reference/COND: Difference between revisions
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The <code>COND</code> command performs a conditional assignment. | The <code>COND</code> command performs a conditional assignment. | ||
Generally, the conditional assignment takes the following form: | Generally, the conditional assignment takes the following form: | ||
target := COND condition ? expr1 : expr2 | |||
<code>target | ;<code>target</code>: is a normal assignment target, usually the name of an S_TOOLS-STx variable, e.g. "#var". | ||
;<code>condition</code>: is a conditional expression like used with the <code>[[User Guide/Workspace/Parameter Processing|IF]]</code> statement and the miscellaneous loop commands, e.g. the string "<code>$#a == 7 || $#a == 42</code>" (for more examples, see the <code>[[User Guide/Workspace/Parameter Processing|IF]]</code> statement). | |||
:Note that with conditional S_TOOLS-STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both "<code>$#a == 7</code>" and "<code>'$#a'=='7'</code>" are valid expression whereas "<code>$#a==7</code>" is not. | |||
;<code>expr1</code> and <code>expr2</code>: Both <code>expr1</code> and <code>expr2</code> may be any expressions that may be normally used in an S_TOOLS-STx "<code>:=</code>" assignment, with the only exception of a <code>COND</code> expression (meaning that conditional assignments must not be nested for the time being). If, at runtime, the conditional expression <code>condition</code> evaluates to truth, the value determined by the first expression, <code>expr1</code>, will be assigned to <code>target</code>. If "<code>condition</code>" evaluates to falsehood, it will be the second expression, <code>expr2</code>, that gets assigned to target. | |||
Note that with conditional S_TOOLS-STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both "<code>$#a == 7</code>" and "<code>'$#a'=='7'</code>" are valid expression whereas "<code>$#a==7</code>" is not. | |||
Both | |||
You may use any S_TOOLS-STx conditional expression you like for "<code>condition</code>". Equally, there is no restriction on "<code>expr1</code>" and "<code>expr2</code>", except that they must not be built up from "<code>COND</code>" expressions themselves. It is even (and also) possible to use command substitutions ("<code>$(...)</code>"), nesting them as deeply as one feels inclined to. | You may use any S_TOOLS-STx conditional expression you like for "<code>condition</code>". Equally, there is no restriction on "<code>expr1</code>" and "<code>expr2</code>", except that they must not be built up from "<code>COND</code>" expressions themselves. It is even (and also) possible to use command substitutions ("<code>$(...)</code>"), nesting them as deeply as one feels inclined to. | ||
Revision as of 16:18, 14 March 2011
The COND command performs a conditional assignment.
Generally, the conditional assignment takes the following form:
target := COND condition ? expr1 : expr2
target- is a normal assignment target, usually the name of an S_TOOLS-STx variable, e.g. "#var".
condition- is a conditional expression like used with the
IFstatement and the miscellaneous loop commands, e.g. the string "$#a == 7 || $#a == 42" (for more examples, see theIFstatement). - Note that with conditional S_TOOLS-STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both "
$#a == 7" and "'$#a'=='7'" are valid expression whereas "$#a==7" is not. expr1andexpr2- Both
expr1andexpr2may be any expressions that may be normally used in an S_TOOLS-STx ":=" assignment, with the only exception of aCONDexpression (meaning that conditional assignments must not be nested for the time being). If, at runtime, the conditional expressionconditionevaluates to truth, the value determined by the first expression,expr1, will be assigned totarget. If "condition" evaluates to falsehood, it will be the second expression,expr2, that gets assigned to target.
You may use any S_TOOLS-STx conditional expression you like for "condition". Equally, there is no restriction on "expr1" and "expr2", except that they must not be built up from "COND" expressions themselves. It is even (and also) possible to use command substitutions ("$(...)"), nesting them as deeply as one feels inclined to.
Examples:
#min := cond $#a < $#b ? $#a : $#b // calculate minimum of #a and #b #abs := cond $#a < 0 ? num -$#a : $#a // calculate absolute value of #a #abs := cond $#a < 0 ? eval $#a*(-1) : $#a // an alternative to the above #absdiff := cond $#a > $#b ? eval $#a-$#b : eval $#b-$#a // absolute difference #len := cond $(length $#a) > 0 ? length $#a : length $#b // length of #a or, if empty, of #b
See the file conditional_assignment.sts for further working examples.
Notes:
The COND command is processed by the loader, and is therefore not available in the command line interface.
The COND command may not contain a nested COND command.
