At 3:07 PM +0930 9/17/02, Dr Mark H Phillips wrote: >Suppose you have some function > >functn :: Int -> Int >functn i > | i>5 = t * i > | i>0 = t_ * i > | otherwise = 1 > where > t = functn (i-2) > t_ = functn (i-1) > >Notice that t and t_ are really local to a guard, rather >than to the whole guard section. Why then, can't you write: > >functn :: Int -> Int >functn i > | i>5 = t * i > where > t = functn (i-2) > | i>0 = t * i > where > t = functn (i-1) > | otherwise = 1 > >In particular, the above would mean you wouldn't need two names >t and t_, you could just use t for both! > >Am I doing something wrongly, or is there a good reason why >where isn't allowed to be used in this way?
You can get the effect you're after by using let-expressions: > functn :: Int -> Int > functn i > | i>5 = let t = functn (i-2) in t * i > | i>0 = let t = functn (i-1) in t * i > | otherwise = 1 'where' is part of the syntax of definitions, not expressions. This enables a name defined in a where-clause to be used in more than one guarded expression. --Ham -- ------------------------------------------------------------------ Hamilton Richards Department of Computer Sciences Senior Lecturer The University of Texas at Austin 512-471-9525 1 University Station C0500 Taylor Hall 5.138 Austin, Texas 78712-1188 [EMAIL PROTECTED] [EMAIL PROTECTED] ------------------------------------------------------------------ _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
