[Haskell-cafe] Stupid question #852: Strict monad

[Stephan Friedrichs]

Hello Brian,

Brian Hurt wrote:
> 
> [...]
> 
> So today's question is: why isn't there a Strict monad?  Something like:
> 
> data Strict a = X a
> 
> instance Monad Strict where
>     ( >>= ) (X m) f = let x = f m in x `seq` (X x)
>     return a = a `seq` (X a)

unless I am mistaken, this violates the first monad law (see Prelude
documentation)

  return a >>= k  ==  k a

for k = const (return 3) and a = undefined, because

  return undefined >>= _  === _|_

but

  const (return 3) undefined === return 3

Generally speaking, the first monad law only holds for strict functions
in your monad.

> 
> [...]
> 

Happy new year,
Stephan

-- 

Früher hieß es ja: Ich denke, also bin ich.
Heute weiß man: Es geht auch so.

 - Dieter Nuhr