How to use types like this: type a = b -> c in haskell

Question

I want to create a type that stores name and value of a variable,so I did this:

type Variable = String
type Val = Int    
type Store = Variable -> Val

now, how can I use this Store?

for example I want to write a function(fetch) that returns value of a variable according to its Store or a function(initial) to initial all the variables( assign a default value,like 0):

fetch:: Store -> Variable -> Val
initial:: Store

how can I do this?

Answer 1

Your Store type is just an alias for a specific kind of function, I could write one as

constStore :: Store
constStore _ = 1

You could make a more complex one:

lenStore :: Store
lenStore var = length var
-- or
-- lenStore = length

Then fetch is just function application

fetch :: Store -> Variable -> Val
fetch store var = store var