[Haskell-cafe] On to applicative
Vo Minh Thu
noteed at gmail.com
Tue Aug 31 13:50:53 EDT 2010
2010/8/31 michael rice <nowgate at yahoo.com>
> So it's a type constructor, not a type? Could you please provide a simple example of its usage?
Sure, although I'm sure you've come by some already.
-- the identity function
id :: a -> a
-- often, we write it like this:
-- id x = x
-- but here we see the relationship between the ananymous function
syntax and the function type:
id = \x -> x
In fact, if you write in prefix form, it is quite familiar:
f :: (->) Int Bool
e = Either String Float
> --- On Tue, 8/31/10, Vo Minh Thu <noteed at gmail.com> wrote:
> From: Vo Minh Thu <noteed at gmail.com>
> Subject: Re: [Haskell-cafe] On to applicative
> To: "michael rice" <nowgate at yahoo.com>
> Cc: haskell-cafe at haskell.org
> Date: Tuesday, August 31, 2010, 1:17 PM
> 2010/8/31 michael rice <nowgate at yahoo.com>
> > "Learn You a Haskell ..." says that (->) is a type just like Either. Where can I find its type definition?
> You can't define it *in* Haskell as user code. It is a built-in infix
> type constructor (Either or Maybe are type constructors too, not just
> types). In fact, if you want to implement a simple, typed functional
> language, you'll find it is the only built-in type constructor you
> have to implement (as the implementor of the language).
> Show a => a
> is a type too, but you won't find a definition for 'a' or for '=>'.
> All those things are defined by the language.
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