Re: [Haskell-beginners] How to understand the type "ShowS"?

I have found the link of difference list. Maybe this helps. http://www.haskell.org/haskellwiki/Difference_list On Tue, Sep 24, 2013 at 7:54 PM, yi lu wrote:

On Tue, Sep 24, 2013 at 7:47 PM, Shrivats wrote:

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What does `show "asdf"` give you in ghci? What Lyndon showed you was that this function is equivalent to `shows x s = show x ++ s`.

Ah, it works a bit like "++" ?

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Have fun,

Shrivats On Sep 24, 2013 5:09 PM, "yi lu" wrote:

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On Tue, Sep 24, 2013 at 6:54 PM, Lyndon Maydwell wrote:

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Looks like it's a convenience for building up a compositions of "Show"s.

ShowS is indeed a synonym for a function. The type of shows alone isn't enough to figure out how it behaves exactly, but testing it out in GHCi is telling:

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[Prelude] λ :i ShowS type ShowS = String -> String -- Defined in `GHC.Show' [Prelude] λ :i shows shows :: Show a => a -> ShowS -- Defined in `GHC.Show' [Prelude] λ shows "asdf" "qwer" "\"asdf\"qwer"

I don't know the meaning of this result.

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On Tue, Sep 24, 2013 at 8:15 PM, yi lu wrote:

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Prelude> :i ShowS type ShowS = String -> String -- Defined in `GHC.Show'

It is a type of a function? I cannot understand this type, and don't know how to create functions of this type.

And this function "shows"

Prelude> :i shows shows :: Show a => a -> ShowS -- Defined in `GHC.Show'

I don't know how this function works.

Yi

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