A cat-readable Haskell summary

gistfile1.rst

Haskell tries to be a pure functional language, for which these rules apply:

1. All functions only does this: Take input, produce output from it; whenever input is the same, output needs to be the same, nothing else may happen. No exceptions.
2. All functions take only a single argument. No exceptions.

This forbids things like printing to the screen, passing 1 and 1 to the plus function and other useful things. But since Haskell only tries to be pure it allows itself to be a little bit impure and has constructs that are excempt from these rules, so Haskell can be useful. Monads are these constructs.

Monads are the house rules you bring to your Monopoly game to make it fun.