Re: [Haskell-cafe] On to applicative

31 Aug 2010


      2010/8/31 michael rice 
...
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

Cheers,
Thu
...
Michael
--- On Tue, 8/31/10, Vo Minh Thu  wrote:
From: Vo Minh Thu 
Subject: Re: [Haskell-cafe] On to applicative
To: "michael rice" 
Cc: haskell-cafe@haskell.org
Date: Tuesday, August 31, 2010, 1:17 PM
2010/8/31 michael rice 
...
"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).
Also,
  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.
Cheers,
Thu