[Haskell-cafe] Proposal: Non-recursive let

Andreas Abel andreas.abel at ifi.lmu.de
Mon Jul 22 10:27:38 CEST 2013

On 20.07.13 9:36 PM, Evan Laforge wrote:
> However, I'm also not agitating for a non-recursive let, I think that
> ship has sailed.  Besides, if it were added people would start
> wondering about non-recursive where, and it would introduce an
> exception to haskell's pretty consistently order-independent
> declaration style.

For functions, recursive-by-default let makes sense.  But for *values*, 
intended recursion is rather the exception.  It is useful for infinite 
lists and the like.  For values of atomic type like Int or Bool, 
recursive let is a bug.

Of course, if you want to do scope-checking before type-checking, which 
also makes sense, you cannot make recursiveness type-dependent.

Distinguishing 'let' into 'fun', 'val' and 'val rec' could help here:


   val x = e
   in  e'


   fun f x = e
   in  e'

   val rec x = e(x)
   in  e'

Andreas Abel  <><      Du bist der geliebte Mensch.

Theoretical Computer Science, University of Munich
Oettingenstr. 67, D-80538 Munich, GERMANY

andreas.abel at ifi.lmu.de

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