public SubstMap unify(final Loc loc, final Type other, final TypeEnv env) {
if (env.checkVisited(this, other)) return SubstMap.EMPTY;
if (other instanceof TypeVar) return SubstMap.bindVar(loc, (TypeVar) other, this);
// if our application expression can be evaluated, unify against that.
if (isAbsApply()) return eval().unify(loc, other, env);
final Type otherEval = other.deref().eval();
if (otherEval instanceof TypeApp) {
final TypeApp otherApp = (TypeApp) otherEval;
final SubstMap baseSubst = base.unify(loc, otherApp.base, env);
if (baseSubst != null) {
final SubstMap argSubst =
arg.subst(baseSubst).unify(loc, otherApp.arg.subst(baseSubst), env);
if (argSubst != null) return baseSubst.compose(loc, argSubst);
}
} else if (kind.equals(otherEval.getKind())) {
// other is not an application expression, but kinds match.
// other type classes do opportunistic matching of type apps
// implementations of unify. This approach is really ad-hoc,
// needs to be rationalized.
return otherEval.unify(loc, this, env);
}
return null;
}
