==== ISTRUE ====
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<callout type="primary" color="" icon="fa fa-book" title="Synopsis">
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Test if an object differs from the null element of its type
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<callout color="green" icon="fa fa-indent" title="Stack Diagram">
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^  __Input Stack__  ^  ^  __Output Stack__  ^
|  **O**  |  **→**  |  **1/0**  |
|  //Level 1 / Argument 1//  |  //→//  |  //Level 1//  | 

{{page>manual:chapter6:aux:legend&nofooter&noeditbtn&inline}}

|**Type**| [[manual:chapter5:basics#operators|Operator]]  ||
|**Parallel list processing**| [[manual:chapter5:listproc#group-2commands-that-must-use-dolist-to-parallel-process|Group 2]]  || 
|**Affected by flags**| None  ||
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<callout color="orangered" icon="fa fa-comment" title="Description">
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The ''ISTRUE'' operator tests implicitly the object on level 1 against the null element of its type and returns ''1'' if it differs or ''0'' otherwise. For each type, the  null element is defined as follows:

^ Type  ^ Null Element  ^
| [[manual:chapter3:reals#approximate-versus-exact|Real]], [[manual:chapter3:reals#approximate-versus-exact|Integer]] or [[manual:chapter3:reals#numbers-in-other-bases|Binary number]]  | ''0'' / ''#0b'' / ''#0o'' / ''#0h''  |
| [[manual:chapter3:complex|Complex number]]  | ''(0,0)'' / ''(0,∡0°)'' / ''(0,∡0r)'' / ''(0,∡0g)'' / ''(0,∡0d)''  |
| [[manual:chapter3:angles|Angle]]  | ''∡0°'' / ''∡0r'' / ''∡0g'' / ''∡0d''  |
| [[manual:chapter3:strings|String]]  | ''""''  |
| [[manual:chapter3:lists|List]]  | ''{ }''  |
| [[manual:chapter3:matrix|Vector]] or [[manual:chapter3:matrix|Matrix]]  | A vector or a matrix where ''ISTRUE'' returns ''0'' for each element  |
| [[manual:chapter3:units|Unit]]  | A unit object with numerical part equal to ''0''  |
| [[manual:chapter4:dirs#variable-storage|Identifier]]  | ''%%'%%ISTRUE(identifier)%%'%%'' FIXME  |
| [[manual:chapter3:symbolic|Symbolic expression]]  | ''%%'%%ISTRUE(expression)%%'%%'' FIXME  |
| [[manual:chapter3:grobs|Grob]]  | No null element. ''ISTRUE'' always returns ''1''  |
| [[manual:chapter3:fonts|Font]]  | No null element. ''ISTRUE'' always returns ''1'' FIXME  |
| [[manual:chapter3:bindata|Binary data container]]  | No null element. ''ISTRUE'' always returns ''1''  |
| [[manual:chapter4:dirs#directories|Directory]]  | No null element. ''ISTRUE'' always returns ''1''  |
| [[manual:chapter4:libs|Library]]  | No null element. ''ISTRUE'' always returns ''1''  |
| [[manual:chapter5|Program]]  | Program gets ''[[manual:chapter6:operators:cmd_ovr_xeq|XEQ]]''%%'%%ted and result is fed to ''ISTRUE'' FIXME  |
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<callout type="danger" icon="true" title="Compatibility">
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This command is new in newRPL and does not exist in userRPL.
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<callout type="info" icon="true" title="Usage">
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<code>
1:           [ [ 0 0 ] [ 0 1 ] ]
……………………………………………………………………………………
ISTRUE
</code>
will result in
<code>
1:                             1
……………………………………………………………………………………

</code>
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<code>
1:           [ [ 0 0 ] [ 0 0 ] ]
……………………………………………………………………………………
ISTRUE
</code>
will result in
<code>
1:                             0
……………………………………………………………………………………

</code>
</callout>

<callout color="darkgray" icon="fa fa-hand-o-right" title="Related Commands">
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{{page>manual:chapter6:operators&nofooter&noeditbtn&inline}}
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