System Labels: Difference between revisions

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     <table border="0" cellpadding="5" cellspacing="0" summary="">
     <table border="0" cellpadding="5" cellspacing="0" summary="">
     <tr>
     <tr>
       <td valign="top"><apll>⎕PROTOTYPE:</apll></td>
       <td valign="top"><apll>⎕PRO:</apll></td>
       <td></td>
       <td></td>
       <td></td>
       <td></td>
Line 12: Line 12:
     </tr>
     </tr>
     <tr>
     <tr>
       <td valign="top"><apll>⎕IDENTITY:</apll></td>
       <td valign="top"><apll>⎕ID:</apll></td>
       <td></td>
       <td></td>
       <td></td>
       <td></td>
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<apll>&nbsp;&nbsp;&nbsp;&nbsp;∇ Z←L foo R<br />
<apll>&nbsp;&nbsp;&nbsp;&nbsp;∇ Z←L foo R<br />
[1]&nbsp;&nbsp;&nbsp;Z←L,R ⋄ →0<br />
[1]&nbsp;&nbsp;&nbsp;Z←L,R ⋄ →0<br />
[2]&nbsp;&nbsp;&nbsp;⎕PROTOTYPE:Z←'Prototype' ⋄ →0<br />
[2]&nbsp;&nbsp;&nbsp;⎕PRO:Z←'Prototype' ⋄ →0<br />
[3]&nbsp;&nbsp;&nbsp;⎕IDENTITY:Z←'Identity'<br />
[3]&nbsp;&nbsp;&nbsp;⎕ID:Z←'Identity'<br />
&nbsp;&nbsp;&nbsp;&nbsp;∇<br /></apll>
&nbsp;&nbsp;&nbsp;&nbsp;∇<br /></apll>


<apll>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;⎕fmt foo/⍳0<br />
<apll>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;⎕fmt foo/<br />
┌──────────┐<br />
┌──────────┐<br />
│┌8───────┐│<br />
│┌8───────┐│<br />
Line 39: Line 39:
┌0──────────┐<br />
┌0──────────┐<br />
│┌9────────┐│<br />
│┌9────────┐│<br />
││Prototype││<br />
││&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;││<br />
│└─────────┘2<br />
│└─────────┘2<br />
└∊──────────┘<br /></apll>
└∊──────────┘<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;foo/¨0⍴⊂⍬<br />
NONCE ERROR<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;foo/¨0⍴⊂⍬<br />
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;∧</apll>


* <p>In the Identity element case, the function is called with the reduction function's right argument prototype as the right argument to the user-defined function/operator; the left argument is undefined.  For example, in <apll>foo/3 0⍴⊂⍳4</apll>, the (right) argument passed to the function is <apll>0 0 0 0</apll>.  The return value from the function is used as the common item in the result.  Thus, the <apll>⎕IDENTITY</apll> entry point is called only once even though the result may have multiple copies of the return value.</p>
* <p>In the Identity element case, the function is called with the reduction function's right argument prototype as the right argument to the user-defined function/operator; the left argument is undefined.  For example, in <apll>foo/3 0⍴⊂⍳4</apll>, the (right) argument passed to the function is <apll>0 0 0 0</apll>.  The return value from the function is used as the common item in the result.  Thus, the <apll>⎕ID</apll> entry point is called only once even though the result may have multiple copies of the return value.</p>


* <p>In the Prototype case, the user-defined function/operator is called with arguments that are the prototypes of the respective arguments; in the monadic case, the left argument is undefined.</p>
* <p>In the Prototype case, the user-defined function/operator is called with arguments that are the prototypes of the respective arguments; in the monadic case, the left argument is undefined.</p>
* <p>For the moment, if two or more System Labels would be called at the same time (such as the last example above), a <apll>NONCE ERROR</apll> is signaled.</p>

Revision as of 22:49, 29 August 2010

Normally, execution of a user-defined function/operator starts execution at line one. However, in certain contexts, execution may start at a different line depending upon the context and the presence of a System Label. These special labels start with a quad symbol so as to present no confusion with normal labels. The following table lists the system labels defined so far and the special context in which they are used.

⎕PRO: is called where a prototype element is needed as in foo¨R where R is empty, or L foo¨R where one of both of L or R is empty and the other is conformable.
⎕ID: is called where an identity element is needed as in foo/R where R is empty.


For example,

    ∇ Z←L foo R
[1]   Z←L,R ⋄ →0
[2]   ⎕PRO:Z←'Prototype' ⋄ →0
[3]   ⎕ID:Z←'Identity'
    ∇

      ⎕fmt foo/⍬
┌──────────┐
│┌8───────┐│
││Identity││
│└────────┘2
└∊─────────┘
      ⎕fmt 1 foo¨⍬
┌0──────────┐
│┌9────────┐│
││         ││
│└─────────┘2
└∊──────────┘
      foo/¨0⍴⊂⍬
NONCE ERROR
      foo/¨0⍴⊂⍬
         ∧

  • In the Identity element case, the function is called with the reduction function's right argument prototype as the right argument to the user-defined function/operator; the left argument is undefined. For example, in foo/3 0⍴⊂⍳4, the (right) argument passed to the function is 0 0 0 0. The return value from the function is used as the common item in the result. Thus, the ⎕ID entry point is called only once even though the result may have multiple copies of the return value.

  • In the Prototype case, the user-defined function/operator is called with arguments that are the prototypes of the respective arguments; in the monadic case, the left argument is undefined.

  • For the moment, if two or more System Labels would be called at the same time (such as the last example above), a NONCE ERROR is signaled.