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.
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