[pure-lang-svn] SF.net SVN: pure-lang: [289] pure/trunk/pure.1.in

[<ag...@us...>]

Revision: 289
          http://pure-lang.svn.sourceforge.net/pure-lang/?rev=289&view=rev
Author:   agraef
Date:     2008-06-23 04:10:39 -0700 (Mon, 23 Jun 2008)

Log Message:
-----------
Add some remarks about implementation restrictions of 'as' patterns.

Modified Paths:
--------------
    pure/trunk/pure.1.in

Modified: pure/trunk/pure.1.in
===================================================================
--- pure/trunk/pure.1.in	2008-06-23 10:26:04 UTC (rev 288)
+++ pure/trunk/pure.1.in	2008-06-23 11:10:39 UTC (rev 289)
@@ -1185,6 +1185,28 @@
 them around as function values or partial applications, but in this case they
 lose all their special call-by-name argument processing.
 .PP
+.B ``As'' patterns.
+In the current implementation, ``as'' patterns cannot be placed on the
+``spine'' of a function definition. Thus rules like the following, which have
+the pattern somewhere in the head of the left-hand side, will all provoke an
+error message from the compiler:
+.sp
+.nf
+a@foo x y   = a,x,y;
+a@(foo x) y = a,x,y;
+a@(foo x y) = a,x,y;
+.fi
+.PP
+This is because the spine of a function application is not available when the
+function is called at runtime. ``As'' patterns in pattern bindings are not
+affected by this restriction since the entire value to be matched is available
+at runtime. For instance:
+.sp
+.nf
+> \fBcase\fP bar 99 \fBof\fP y@(bar x) = y,x+1; \fBend\fP;
+bar 99,100
+.fi
+.PP
 .B Manipulating function applications.
 The ``head = function'' rule means that the head symbol f of an application f
 x1 ... xn occurring on (or inside) the left-hand side of an equation, pattern


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