[Haskell-cafe] Type checking with Haskell

Folks, The ghc/compiler/typecheck directory holds a rather large body of code and quick browsing through did not produce any insight. How do you implement type checking in haskell? Assume I have an Expr type with a constructor per type and functions can take lists of expressions. Do I create a function taking an Expr, pattern-matching on appropriate constructor and returning True on a match and False otherwise? Thanks, Joel -- http://wagerlabs.com/