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

[David McBride]

ShowS is just a type alias for String -> String.  Anywhere where you could
put a function of type String -> String you could replace that with ShowS.
Examples

blah :: String -> String
blah "abc" = "def"

is no different than

blah :: Shows
blah "abc" = "def"

>From the GHC.Show import

GHC.Show.showList__ :: (a -> ShowS) -> [a] -> ShowS

is equivalent to

GHC.Show.showList__ :: (a -> (String -> String)) -> [a] -> (String ->
String)

It can be a little confusing but a lot of times you use the same function
prototype and it is useful to just turn it into its own little type to
shorten the types in your code.


On Tue, Sep 24, 2013 at 6:15 AM, yi lu <zhiwudazhanjiangshi at gmail.com>wrote:

> 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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