==== EVAL ====
----
<callout type="primary" color="" icon="fa fa-book" title="Synopsis">
----
Evaluate an object, recursively
</callout>

<callout color="green" icon="fa fa-indent" title="Stack Diagram">
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^  __Input Stack__  ^  ^  __Output Stack__  ^^^
|  **O**  |  **→**  |  //see list under __Description__//  |||
|  //Level 1//  |  //→//  |  //Level n//  |  //...//  |  //Level 1//  | 

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|**Type**| [[manual:chapter5:basics#operators|Operator]]  ||
|**Parallel list processing**| //Yes, but specific group is determined by the object being evaluated//  || 
|**Affected by flags**|  [[manual:appendix:flags#flag-70|-70]] | Global autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-71|-71]] | Application of **Group 1** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-72|-72]] | Application of **Group 2** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-73|-73]] | Application of **Group 3** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-74|-74]] | Application of **Group 4** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-75|-75]] | Application of **Group 5** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-76|-76]] | Application of **Group 6** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-77|-77]] | Application of **Group 7** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-78|-78]] | Application of **Group 8** autosimplification rules  |
|:::|  [[manual:appendix:flags#flag-103|-103]] | Complex results  |
</callout>

<callout color="orangered" icon="fa fa-comment" title="Description">
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The ''EVAL'' command evaluates the object on the top level of the stack. Evaluation occurs //recursively//.

The effect of the evaluation and the resulting output depends on the type of object being evaluated, as summarized by the following list.

  * **Local Name**: ''EVAL'' //recalls// the content of the variable.
  * **Global Name**: ''EVAL'' //calls// the content of a variable:
    - a __Name__ is ''EVAL''uated;
    - a __Program__ is ''EVAL''uated;
    - a __Directory__ becomes the current directory;
    - __other objects__ which are not lists are put on the stack.
  * **Program**: ''EVAL'' //enters// each object in the program:
    - an [[manual:chapter6:dirs:cmd_unquoteid|unquoted]] __Name__ is ''EVAL''uated;
    - a __Keyword__ is ''[[manual:chapter6:operators:cmd_ovr_xeq|XEQ]]''ted;
    - __other objects__ which are not lists are put on the stack.
  * **Symbolic expression**: ''EVAL'' //enters// each object in the expression:
    - a __Name__ is ''EVAL''uated;
    - a __Keyword__ is ''[[manual:chapter6:operators:cmd_ovr_xeq|XEQ]]''ted;
    - __other objects__ which are not lists are put on the stack.
  * **Other objects**: if they are not lists ''EVAL'' puts them on the stack.
  * **List**: ''EVAL'' //enters// each object in the list:
    - __any object__ is ''EVAL''uated according above mentioned rules.
    
As a final step, ''EVAL'' will perform numerical simplification according to the status of flags from [[manual:appendix:flags#flag-70|-70]] to [[manual:appendix:flags#flag-78|-78]].
</callout>

<callout type="warning" icon="true" title="Compatibility">
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This command is only partially compatible with userRPL.

In particular:

  * In userRPL, if the argument is a list ''EVAL'' //enters// any object in the list, then:
    - a __Name__ is ''EVAL''uated;
    - a __Program__ is ''EVAL''uated;
    - a __Keyword__ is ''[[manual:chapter6:operators:cmd_ovr_xeq|XEQ]]''ted;
    - __other objects__ are put on the stack.
    
    while in newRPL, [[manual:chapter5:listproc#parallel-processing-with-lists|parallel list processing]] is performed.
</callout>

<callout type="info" icon="true" title="Usage">
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If the following commands are executed
<code>
2:                          6.28
1:                       'TWOPI'
……………………………………………………………………………………
STO
</code>

<code>
2:                   « TWOPI * »
1:                      'CIRCUM'
……………………………………………………………………………………
STO
</code>
then the command
<code>
2:                             2
1:                      'CIRCUM'
……………………………………………………………………………………
EVAL
</code>
will perform the following steps:
  - ''CIRCUM'' (a //global name//) is ''EVAL''uated;
  - ''« TWOPI * »'' (a //program//) is ''EVAL''uated;
  - ''TWOPI'', the first object (a //global name//) in the program is ''EVAL''uated;
  - ''6.28'' (a //real number//) is put on the stack;
  - ''[[manual:chapter6:operators:cmd_ovr_mul|*]]'', the second object (a //keyword//) in the program is ''[[manual:chapter6:operators:cmd_ovr_xeq|XEQ]]''ted.

Resulting in
<code>
1:                         12.56
……………………………………………………………………………………

</code>
----
The command
<code>
1:                    { '16' √ }
……………………………………………………………………………………
EVAL
</code>
will perform the following steps:
  - ''%%'16'%%'' (a //symbolic expression//) is ''EVAL''uated;
  - ''16'' (a //real number//) is put on the stack;
  - ''[[manual:chapter6:transcendentals:cmd_sqrt|√]]'' (a //keyword//) is ''[[manual:chapter6:operators:cmd_ovr_xeq|XEQ]]''ted.

Resulting in
<code>
1:                        { 4. }
……………………………………………………………………………………

</code>
</callout>

<callout color="darkgray" icon="fa fa-hand-o-right" title="Related Commands">
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</callout>