[Haskell-cafe] Re: Type errors, would extensions help?

Lennart Augustsson lennart at augustsson.net
Thu Jan 15 18:26:37 EST 2009

The <- binding is lambda binding (look at how it desugars).  Lambda
bindings are monomorphic without any type extensions.  The monadic
'let' binding is like regular 'let', so it's a point where the type
checker does generalization, and so you get (possibly) polymorphic
bindings from let.

  -- Lennart

On Thu, Jan 15, 2009 at 11:20 PM, Mauricio <briqueabraque at yahoo.com> wrote:
> Thanks, everything works now.
> What should I read to better understand the difference
> for the type system between using <- and 'let'? That is
> not intuitive for me.
> About layout, I used to filter my code to better fit
> everyone taste before posting to this list. The filter
> stoped working due to some problems in 'Language.Haskell',
> but I'll rewrite it with haskell-src-exts before
> posting again.
> Thanks,
> Maurício
>> I suggest you start using "let" in your do blocks; both of these
>> problems are solvable with let.
>> Binding with <- instead of "let" makes the type system work harder,
>> and will generally require type annotations & extensions for
>> polymorphic results.  (...)
>> Also, is there a reason you hate the layout rule and are using
>> explicit semicolons everywhere?
>>>>> I have this problem trying to define a function
>>>>> inside a do expression. (...)
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