Okay, I have found the missing definition (code was split by page break), and found the type error: type Subst = [(Var,Term)] should be: type Subst = [(Vname,Term)] And have written a simple implementation of unify from a description of the algorithm. I was wondering if anyone has any comments on my implementation of unify? For example can the algorithm be simplified from my nieve attempt? Most importantly is it correct? type Subst = [(Vname,Term)] data Term = Func Fname [Term] | Var Vname deriving (Eq,Show) type Fname = String data Vname = Name String | Auto Integer deriving (Eq,Show) unify :: Subst -> (Term,Term) -> [Subst] unify s (t,u) | t == u = [s] unify s (Var x,t) = [(x,t):s] -- no occurs check unify s (t,Var x) = [(x,t):s] -- no occurs check unify s (Func f ts,Func g us) | f == g = unify' s ts us | otherwise = [] unify' :: Subst -> [Term] -> [Term] -> [Subst] unify' s [] [] = [s] unify' s (t0:ts) (u0:us) = case unify s (t0,u0) of s@(_:_) -> unify' (concat s) ts us _ -> [] Keean. Keean Schupke wrote:
Does anyone know if the source code for the embedded prolog (by Silvija Seres & Michael Spivey) is available for download from anywhere? I have read the paper and found some of the types are wrong, some critical definitions are missing, and the definition of unify is missing.