Haskell (with the GHC compiler) is a lot faster than you'd expect. Used correctly, it can get close-ish to low-level languages. (A favorite thing for Haskellers to do is to try and get within 5% of C (or even beat it, but that means you are using an inefficient C program, since GHC compiles Haskell to C).) My question is, why?

Haskell is declarative and based on lambda calculus. Machine architectures are clearly imperative, being based on turing machines, roughly. Indeed, Haskell doesn't even have a specific evaluation order. Also, instead of dealing with machine data types, you make algebraic data types all the time.

Weirdest of all though is higher order functions. You would think that creating functions on the fly, and throwing them around, would make a program slower. But using higher order functions actually makes Haskell faster. Indeed, it seems that, to optimize Haskell code, you need to make it more elegant and abstract instead of more machine-like. None of Haskell's more advanced features seem to even affect its performance, if they don't improve it.

Sorry if this is sounding ranty, but here is my question: Why is Haskell (compiled with GHC) so fast, considering its abstract nature and differences from physical machines?

Note: The reason I say C and other imperative languages are somewhat similar to Turing Machines (but not to the extent that Haskell is similar to Lambda Calculus) is that in an imperative language, you have a finite number of states (a.k.a. line number), along with a Tape (the ram), such that the state and the current tape determine what to do to the tape. See the Wikipedia entry, Turing machine equivalents, for the transition from Turing Machines to computers.

I am so glad that you know about Haskell. :)