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. | ||
==Usage== | ==Usage== | ||
[ <var>target</var> := ] COND [[Programmer_Guide/Introduction#Conditional_Expressions|condition]] ? <var>expr1</var> : <var>expr2</var> | |||
;<var>target</var>: is a normal assignment target, usually the name of an {{STX}} variable, e.g. <code>#var</code>. If no target is specified, a conditional execution is performed. | ;<var>target</var>: is a normal assignment target, usually the name of an {{STX}} variable, e.g. <code>#var</code>. If no target is specified, a conditional execution is performed. | ||
;<var>condition</var>: is a [[Programmer_Guide/Introduction#Conditional_Expressions|conditional expression]] like used with the <code>[[Programmer_Guide/Command_Reference|IF]]</code> statement and the miscellaneous conditional [[Programmer_Guide/Introduction#Control_Commands|control commands]]. | ;<var>condition</var>: is a [[Programmer_Guide/Introduction#Conditional_Expressions|conditional expression]] like used with the <code>[[Programmer_Guide/Command_Reference|IF]]</code> statement and the miscellaneous conditional [[Programmer_Guide/Introduction#Control_Commands|control commands]]. | ||
: | :Note that with conditional {{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. | ||
;<var> | ;<var>expr<sub>1</sub></var>, <var>expr<sub>2</sub></var>: Both <code>expr<sub>1</sub></code> and <code>expr<sub>2</sub></code> may be any commands, with the only exception of all control commands. If, at runtime, the conditional expression <var>condition</var> evaluates to truth, the first command <var>expr<sub>1</sub></var> will be executed, otherwise the second <var>expr<sub>2</sub></var>. If <var>target</var> is specified, the return value of the executed command is assigned. | ||
==Notes== | ==Notes== | ||
* The <code>COND</code> command is processed by the loader, and is therefore not available in the command line interface. | * The <code>COND</code> command is processed by the loader, and is therefore not available in the command line interface. | ||
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#absdiff := cond $#a > $#b ? eval $#a-$#b : eval $#b-$#a // absolute difference | #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 | #len := cond $(length $#a) > 0 ? length $#a : length $#b // length of #a or, if empty, of #b | ||
cond '$#item[?]' == table ? gosub useTable $#item : gosub useOtherItem $#item | |||
See the file <code>conditional_assignment.sts</code> for further working examples. | See the file <code>conditional_assignment.sts</code> for further working examples. | ||
<!-- C.G. 14.3.2011 --> | <!-- C.G. 14.3.2011 --> | ||
<!-- A.N. 27.4.2011 --> | <!-- A.N. 27.4.2011 --> | ||
Latest revision as of 16:26, 24 April 2014
The COND command performs a conditional assignment.
Usage
[ target := ] COND condition ? expr1 : expr2
- target
- is a normal assignment target, usually the name of an STx variable, e.g.
#var. If no target is specified, a conditional execution is performed. - condition
- is a conditional expression like used with the
IFstatement and the miscellaneous conditional control commands. - Note that with conditional STx expressions there must always be intervening whitespaces between operators and their arguments (unless the argument is quoted). So, both
$#a == 7and'$#a'=='7'are valid expression, whereas$#a==7is not. - expr1, expr2
- Both
expr1andexpr2may be any commands, with the only exception of all control commands. If, at runtime, the conditional expression condition evaluates to truth, the first command expr1 will be executed, otherwise the second expr2. If target is specified, the return value of the executed command is assigned.
Notes
- The
CONDcommand is processed by the loader, and is therefore not available in the command line interface. - The
CONDcommand may not contain a nestedCONDcommand.
See also
conditonal assignment with EVAL, control commands, IF
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 $#b // length of #a or, if empty, of #b
cond '$#item[?]' == table ? gosub useTable $#item : gosub useOtherItem $#item
See the file conditional_assignment.sts for further working examples.
