Is everything in Haskell stored in thunks, even simple values?

Question

What do the thunks for the following value/expression/function look like in the Haskell heap?

val = 5                -- is `val` a pointer to a box containing 5?         


        

Answer 1

I think the others answered your question nicely, but just for completeness's sake let me add that GHC offers you the possibility of using unboxed values directly as well. This is what Haskell Wiki says about it:

When you are really desperate for speed, and you want to get right down to the “raw bits.” Please see GHC Primitives for some information about using unboxed types.

This should be a last resort, however, since unboxed types and primitives are non-portable. Fortunately, it is usually not necessary to resort to using explicit unboxed types and primitives, because GHC's optimiser can do the work for you by inlining operations it knows about, and unboxing strict function arguments. Strict and unpacked constructor fields can also help a lot. Sometimes GHC needs a little help to generate the right code, so you might have to look at the Core output to see whether your tweaks are actually having the desired effect.

One thing that can be said for using unboxed types and primitives is that you know you're writing efficient code, rather than relying on GHC's optimiser to do the right thing, and being at the mercy of changes in GHC's optimiser down the line. This may well be important to you, in which case go for it.

As mentioned, it's non-portable, so you need a GHC language extension. See here for their docs.