tparam := NewTypeParam(NewTypeName(nopos, nil, "P", nil), &emptyInterface)
		params := NewTuple(NewVar(nopos, nil, "_", tparam))
		unaryP = NewSignatureType(nil, nil, []*TypeParam{tparam}, params, nil, false)
	}

	ctxt := NewContext()

	// Update the context with an instantiation of nullaryP.
	inst := NewSignatureType(nil, nil, nil, nil, nil, false)
	if got := ctxt.update("", nullaryP, []Type{Typ[Int]}, inst); got != inst {
		t.Error("bad")
	}

		tparam := NewTypeParam(NewTypeName(nopos, nil, "P", nil), &emptyInterface)
		params := NewTuple(NewVar(nopos, nil, "_", tparam))
		unaryP = NewSignatureType(nil, nil, []*TypeParam{tparam}, params, nil, false)
	}

	ctxt := NewContext()

	// Update the context with an instantiation of nullaryP.
	inst := NewSignatureType(nil, nil, nil, nil, nil, false)
	if got := ctxt.update("", nullaryP, []Type{Typ[Int]}, inst); got != inst {
		t.Error("bad")
	}

//
// StructuralTerms makes no guarantees about the order of terms, except that it
// is deterministic.
func StructuralTerms(tparam *types.TypeParam) ([]*types.Term, error) {
	constraint := tparam.Constraint()
	if constraint == nil {
		return nil, fmt.Errorf("%s has nil constraint", tparam)
	}
	iface, _ := constraint.Underlying().(*types.Interface)
	if iface == nil {

      case NONE:
        return true;
    }
  }

  /// @brief Implements visitor pattern for doing type-based dispatch.
  ///
  /// @tparam R The desired return type.
  /// @tparam Visitor The visitor class which has a callable operator.
  /// @return The `visitor` called on the correct value.
  template <class R, class Visitor>
  R visit(Visitor visitor) {
    switch (type_) {

	// example by renaming the type parameter P into P2.
	if len(tparams) == 0 {
		return nil, typ // nothing to do
	}

	tparams2 := make([]*TypeParam, len(tparams))
	for i, tparam := range tparams {
		tname := NewTypeName(tparam.Obj().Pos(), tparam.Obj().Pkg(), tparam.Obj().Name(), nil)
		tparams2[i] = NewTypeParam(tname, nil)
		tparams2[i].index = tparam.index // == i
	}

	renameMap := makeRenameMap(tparams, tparams2)

	// example by renaming the type parameter P into P2.
	if len(tparams) == 0 {
		return nil, typ // nothing to do
	}

	tparams2 := make([]*TypeParam, len(tparams))
	for i, tparam := range tparams {
		tname := NewTypeName(tparam.Obj().Pos(), tparam.Obj().Pkg(), tparam.Obj().Name(), nil)
		tparams2[i] = NewTypeParam(tname, nil)
		tparams2[i].index = tparam.index // == i
	}

	renameMap := makeRenameMap(tparams, tparams2)

				return nil, fmt.Errorf("cannot apply %q to %s (got %T, want named or signature)", code, t, t)
			}
			tparams := hasTypeParams.TypeParams()
			if n := tparams.Len(); index >= n {
				return nil, fmt.Errorf("tuple index %d out of range [0-%d)", index, n)
			}
			t = tparams.At(index)

		case opConstraint:
			tparam, ok := t.(*types.TypeParam)
			if !ok {

				// hasher.
				ptrMap:     h.ptrMap,
				sigTParams: tparams,
			}
		}

		for i := 0; i < tparams.Len(); i++ {
			tparam := tparams.At(i)
			hash += 7 * h.Hash(tparam.Constraint())
		}

		return hash + 3*h.hashTuple(t.Params()) + 5*h.hashTuple(t.Results())

	case *types.Union:
		return h.hashUnion(t)

	case *types.Interface:

			}
		}

		tparam := pkg.formatTypeParams(n.TypeParams, depth)
		param := joinStrings(params)
		if len(results) == 0 {
			return fmt.Sprintf("func%s(%s)", tparam, param)
		}
		result := joinStrings(results)
		if !needParens {
			return fmt.Sprintf("func%s(%s) %s", tparam, param, result)
		}
		return fmt.Sprintf("func%s(%s) (%s)", tparam, param, result)

	case *ast.StructType:

			// Find the corresponding type argument for the type parameter
			// and proceed with checking that type argument.
			for i, tparam := range inst.TypeParams().list() {
				// The type parameter and type argument lists should
				// match in length but be careful in case of errors.
				if t == tparam && i < inst.TypeArgs().Len() {
					targ := inst.TypeArgs().At(i)
					// The type argument must be valid in the enclosing