env: Unifier

This is a technical class that is used as a marker (a base) for all unifiers. It defines no properties or methods. It is only purpose is to be used in the implementation of isUnifier().

It is defined in env and can be accessed like that:

import {Unifier} from 'deep6/env.js';

The current definition:

class Unifier {}

API

While Unifier does not define any methods it is assumed that supported objects follow the Unifier protocol and define the following method:

• unify(val, ls, rs, env) — a function that returns a boolean value to indicate success/failure of the unification. It takes the following arguments:
  • val — an arbitrary value to unify with.
  • ls — a stack of left arguments waiting to be unified at this point.
  • rs — a stack of right arguments corresponding to ls waiting to be unified at this point.
  • env — an environment to be used to resolve variables.

In most cases, the implementation pushes the appropriate values to ls and rs stacks and returns true leaving the actual unification to be done later.

Example:

// a unifier to test values for 0

class IsZero extends Unifier {
  unify(val, ls, rs, env) {
    // shortcuts
    if (val === 0 || val === any || val instanceof IsZero) return true;
    // actual work
    ls.push(0);
    rs.push(val);
    return true;
  }
}