[Haskell-beginners] basic Functor, Applicative and Monad instances

[amindfv at gmail.com]

You have the types of the functions commented out in the instances. If you use {-# LANGUAGE InstanceSigs #-} you can write them for real (and be sure that they're accurate)

Tom

El Jul 17, 2015, a las 3:53, Imants Cekusins <imantc at gmail.com> escribió:

> based on this snippet and Rein's comment, here is monad file template
> for intellij Idea to make new monads a quick exercise:
> 
> module ${PACKAGE_NAME}.${NAME} where
> 
> 
> data ${Type} a = ${ctor} {
>    ${prop}::a
> }
> 
> 
> instance Functor ${Type} where
> -- (a -> b) -> f a -> f b
> --   fmap f (${ctor} x) = ${ctor} (f x)
>   fmap ab fa = let  a1 = ${prop} fa
>                     b1 = ab a1
>                in fa { ${prop} = b1 }
> 
> 
> instance Applicative ${Type} where
> -- a -> f a
> --  pure = ${ctor}
>   pure a =  ${ctor} { ${prop} = a }
> 
> -- f (a -> b) -> f a -> f b
> --   ${ctor} f <*> ${ctor} x = ${ctor} (f x)
>   (<*>) fab fa =  let  ab1 = ${prop} fab
>                        a1 = ${prop} fa
>                        b1 = ab1 a1
>                   in fa { ${prop} = b1 }
> 
> 
> instance Monad ${Type} where
> -- a -> m a
>   return a = ${ctor} { ${prop} = a }
> 
> --  m a -> (a -> m b) -> m b
>   (>>=) ma amb = let a1 = ${prop} ma
>                 in amb a1
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners