[Haskell] question about a failure to generalize
tom at pledger.gen.nz
Mon Sep 17 01:07:59 EDT 2007
Quoting Stefan O'Rear <stefanor at cox.net>:
> On Mon, Sep 17, 2007 at 04:15:10PM +1200, Tom Pledger wrote:
>> Norman Ramsey wrote:
>> | This code fails to compile because the compiler is willing to
>> | use 'fold' at only one type (CmmExpr as it happens)
>> When it failed to compile, was
>> fold = foldRegsUsed
>> a top-level declaration in the module, rather than local to foldRegsUsed?
>> If so, try working around the monomorphism restriction by changing from a
>> pattern binding to a function binding.
>> fold f = foldRegsUsed f
> The monomorphism restriction is not affected by top-level-or-not, see
> sections 4.5.1 and 4.5.5 in the Haskell 98 Language and Libraries
Aargh! Sorry, I'm having a Bad Details Day. 3 in 1 message:
- Overlooking the "to make the code work, I had to expand 'fold'
into 'foldRegsUsed' everywhere it appears" part in the original
- Chopping a letter out of Norman's email address, and
- Mixing up the MR with other issues, possibly something from the
binding groups section of Typing Haskell In Haskell.
The one saving grace is that I tested my suggestion before posting,
and it worked. :-)
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