Question

I’m trying to figure out if Haskell uses dynamic or static scoping. I realize that, for example, if you define:

let x = 10 

then define the function

let square x = x*x 

You have 2 different ‘x’s’, and does that mean it is dynamically scoped? If not, what scoping does it use, and why?

Also, can Haskell variables have aliases (a different name for the same memory location/value)?

Thanks.

Answer 1

There are some things wrong in your statements…

• There are no mutable variables in Haskell just definitions (or immutable variables)
• A variable memory location is a concept that do not exist in Haskell

In your example, x is not 10 in the function is just a argument to square, that can take any value (you can specify the type later) in this case 10 but just in this case.

Here is an example of aliases provided by Curt Sampson:

import Data.IORef  main :: IO () main = do x <- newIORef 0         -- write 0 into x           readIORef x >>= print   -- x contains 0           let y = x           readIORef y >>= print   -- y contains 0           writeIORef x 42         -- write 42 into x           readIORef y >>= print   -- y contains 42