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I recently began looking at core libraries on Hackage, and there's a recurring idiom I don't understand. Here's an example from the ST module:
instance Monad (ST s) where
{-# INLINE (>>=) #-}
(>>) = (*>)
(ST m) >>= k
= ST (\ s ->
case (m s) of { (# new_s, r #) ->
case (k r) of { ST k2 ->
(k2 new_s) }})
In particular, I don't understand (# new_s, r #). I assume the second hash refers to an unboxed value, but the rest is a mystery to me (something to do with "new state", presumably).
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All the three rules are strictly applicable over a Monad declaration which is as follows − The three basic laws that are applicable over a Monad declaration are − Left Identity Law − The return function does not change the value and it should not change anything in the Monad. It can be expressed as "return >=> mf = mf".
It can be expressed as "return >=> mf = mf". Right Identity Law − The return function does not change the value and it should not change anything in the Monad. It can be expressed as "mf >=> return = mf". Associativity − According to this law, both Functors and Monad instance should work in the same manner.
Syntax of Variable Declaration The word syntax means the grammar of a programming language. We can talk about the syntax of just a small part of a program, such as the syntax of variable declaration. This declares a variable, declares its data type, and reserves memory for it. It says nothing about what value is put in memory.
One generic concept that I love expressing in JS is the functional keystone known as the Monad. A Monad is an encapsulation of an associative binary operation. In other words, you can call map on it with an appropriate function parameter to change the inner value — even its type.
(# x, y, z #) is an unboxed tuple with three elements. See "8.2.2. Unboxed Tuples" at https://downloads.haskell.org/~ghc/6.8.3/docs/html/users_guide/primitives.html.
The rest is basically just an implementation of State.
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