[pure-lang-svn] SF.net SVN: pure-lang:[879] pure/trunk/lib/prelude.pure

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

Revision: 879
          http://pure-lang.svn.sourceforge.net/pure-lang/?rev=879&view=rev
Author:   agraef
Date:     2008-09-27 04:41:02 +0000 (Sat, 27 Sep 2008)

Log Message:
-----------
Simplify definition of cat.

Modified Paths:
--------------
    pure/trunk/lib/prelude.pure

Modified: pure/trunk/lib/prelude.pure
===================================================================
--- pure/trunk/lib/prelude.pure	2008-09-27 04:15:24 UTC (rev 878)
+++ pure/trunk/lib/prelude.pure	2008-09-27 04:41:02 UTC (rev 879)
@@ -452,16 +452,14 @@
 /* Concatenate a list of lists. */
 
 cat []			= [];
-cat xs@(_:_)		= foldr (+) [] xs
+cat xs@(_:_)		= foldr (tick []) [] xs
 with
   /* Unfortunately, the global list concatenation operator (+) isn't fully
      lazy in Pure, because it's also used for arithmetic operations. Using it
      here would make foldr (and hence cat) eager. Therefore we use our own
      concatenation operation here, which properly deals with the case that ys
      is an infinite stream when applied recursively. */
-  []+ys			= ys;
-  xs@(_:_)+ys		= tick [] xs ys;
-  tick zs (x:xs) ys	= tack (x:zs) ((xs+ys)&) if thunkp xs;
+  tick zs (x:xs) ys	= tack (x:zs) (tick [] xs ys&) if thunkp xs;
 			= tick (x:zs) xs ys;
   tick zs [] ys		= tack zs ys;
   tick zs xs ys		= tack zs (xs+ys);


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