[Haskell-beginners] A very counterintuitive behaviour of Haskell

[Jonas Almström Duregård]

> The problem comes from using the interpreter and not from haskell.

But a very similar 'problem' can be achieved in generic Haskell:

x = do
  let f 7 = "yes"
  let f x = "no"
  putStrLn (f 7)

Arguably the compiler could issue a warning here because the second
'let' keyword might be intended to be spaces. I don't know how common
these mistakes are though.

I think the original poster suggests that the shadowing function
should only be used when the original function doesn't match. That is
more problematic if you ask me though.

/J

On 27 January 2011 16:09, jean verdier <verdier.jean at gmail.com> wrote:
> You have defined 2 functions that are called f and only the last
> definition is used (f x = "no").
> The definition you want should be written
> let f 7 = "ok"; f x = "no"
> so the function is defined once.
> The problem comes from using the interpreter and not from haskell.
>
>
> On Thu, 2011-01-27 at 15:55 +0100, Renzo Orsini wrote:
>> In studying Haskell, I produced the following output from GHC:
>>
>> xxx-3:~ xxx$ GHCi
>> GHCi, version 6.12.3: http://www.haskell.org/ghc/  :? for help
>> Loading package ghc-prim ... linking ... done.
>> Loading package integer-gmp ... linking ... done.
>> Loading package base ... linking ... done.
>> Loading package ffi-1.0 ... linking ... done.
>> Prelude> let f 7 = "ok"
>> Prelude> let f x = "no"
>> Prelude> f 3
>> "no"
>> Prelude> f 7
>> "no"
>>
>>
>> I suppose it is correct. However, for someone who is interested in the language, it seems very counterintuitive... Somebody would be so kind to explain to a neophyte this "feature" of the language?
>>
>> Thank you very much.
>>
>> Renzo
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>
>
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