std: rename sub to set and genericize (#190)

* wdte: Rename `sub` to `set` and genercize.

* wdte: Update to work with new `set` function.

std/std.go

@@ -467,17 +467,50 @@ func At(frame wdte.Frame, args ...wdte.Func) wdte.Func {
 	at := args[0].Call(frame).(wdte.Atter)
 	i := args[1].Call(frame)
 
-	ret, ok := at.At(i)
-	if !ok {
+	ret, err := at.At(i)
+	if err != nil {
 		return &wdte.Error{
 			Frame: frame,
-			Err:   fmt.Errorf("index %v out of range", i),
+			Err:   err,
 		}
 	}
 
 	return ret
 }
 
+// Set is a WDTE function with the following signatures:
+//
+//    set con key val
+//    (set val) con key
+//    (set key val) con
+//
+// Set uses con's implementation of Setter to produce a new value from
+// con with a key-val mapping applied to it. For example,
+//
+//    set [1; 2; 3] 1 5
+//
+// returns a new Array containing [1; 5; 3].
+func Set(frame wdte.Frame, args ...wdte.Func) wdte.Func {
+	frame = frame.Sub("set")
+
+	if len(args) < 3 {
+		return wdteutil.SaveArgsReverse(wdte.GoFunc(Set), args...)
+	}
+
+	s := args[0].Call(frame).(wdte.Setter)
+	k := args[1].Call(frame)
+	v := args[2]
+
+	r, err := s.Set(k, v)
+	if err != nil {
+		return &wdte.Error{
+			Frame: frame,
+			Err:   err,
+		}
+	}
+	return r
+}
+
 // Collect is a WDTE function with the following signature:
 //
 //    collect compound
@@ -522,28 +555,6 @@ func Known(frame wdte.Frame, args ...wdte.Func) wdte.Func {
 	return ret
 }
 
-// Sub is a WDTE function with the following signatures:
-//
-//    sub scope id val
-//    (sub val) scope id
-//    (sub id val) scope
-//
-// Sub returns a subscope of scope with the value val bound to the ID
-// id.
-func Sub(frame wdte.Frame, args ...wdte.Func) wdte.Func {
-	if len(args) <= 2 {
-		return wdteutil.SaveArgsReverse(wdte.GoFunc(Sub), args...)
-	}
-
-	frame = frame.Sub("sub")
-
-	s := args[0].Call(frame).(*wdte.Scope)
-	id := wdte.ID(args[1].Call(frame).(wdte.String))
-	v := args[2]
-
-	return s.Add(id, v)
-}
-
 // Reflect is a WDTE function with the following signature:
 //
 //    reflect v type
@@ -592,7 +603,7 @@ var Scope = wdte.S().Map(map[wdte.ID]wdte.Func{
 	"at":      wdte.GoFunc(At),
 	"collect": wdte.GoFunc(Collect),
 	"known":   wdte.GoFunc(Known),
-	"sub":     wdte.GoFunc(Sub),
+	"set":     wdte.GoFunc(Set),
 	"reflect": wdte.GoFunc(Reflect),
 })
 

types.go

@@ -26,9 +26,15 @@ type Lenner interface {
 
 // An Atter is a Func that can be indexed, like an array or a string.
 type Atter interface {
-	// At returns the value at index i. If the index is out of range, it
-	// should return false as its second return value.
-	At(i Func) (Func, bool)
+	At(i Func) (Func, error)
+}
+
+// A Setter is a Func that can produce a new Func from itself with a
+// key-value mapping applied in some way. For example, a scope can
+// produce a subscope with a new variable added to it, or an array can
+// produce a new array with an index modified.
+type Setter interface {
+	Set(k, v Func) (Func, error)
 }
 
 // A Reflector is a Func that can determine if it can be treated as
@@ -85,16 +91,13 @@ func (s String) Len() int { // nolint
 	return len(s)
 }
 
-func (s String) At(i Func) (Func, bool) { // nolint
-	if i, ok := i.(Number); ok {
-		if (int(i) < 0) || (int(i) >= len(s)) {
-			return nil, false
-		}
-
-		return String(s[int(i)]), true
+func (s String) At(index Func) (Func, error) { // nolint
+	i := int(index.(Number))
+	if (i < 0) || (i >= len(s)) {
+		return nil, fmt.Errorf("index %v is out of range [0,%v)", i, len(s))
 	}
 
-	return nil, false
+	return String(s[i]), nil
 }
 
 func (s String) Reflect(name string) bool { // nolint
@@ -158,16 +161,25 @@ func (a Array) Len() int { // nolint
 	return len(a)
 }
 
-func (a Array) At(i Func) (Func, bool) { // nolint
-	if i, ok := i.(Number); ok {
-		if (int(i) < 0) || (int(i) >= len(a)) {
-			return nil, false
-		}
+func (a Array) At(index Func) (Func, error) { // nolint
+	i := int(index.(Number))
+	if (i < 0) || (i >= len(a)) {
+		return nil, fmt.Errorf("index %v is out of range [0,%v)", i, len(a))
+	}
+
+	return a[i], nil
+}
 
-		return a[int(i)], true
+func (a Array) Set(k, v Func) (Func, error) { // nolint
+	i := int(k.(Number))
+	if (i < 0) || (i >= len(a)) {
+		return nil, fmt.Errorf("index %v is out of bounds [0,%v]", i, len(a))
 	}
 
-	return nil, false
+	c := make(Array, len(a))
+	copy(c, a)
+	c[i] = v
+	return c, nil
 }
 
 func (a Array) String() string { // nolint

wdte.go

@@ -354,9 +354,16 @@ func (s *Scope) Call(frame Frame, args ...Func) Func { // nolint
 	return s
 }
 
-func (s *Scope) At(i Func) (Func, bool) { // nolint
+func (s *Scope) At(i Func) (Func, error) { // nolint
 	v := s.Get(ID(i.(String)))
-	return v, v != nil
+	if v == nil {
+		return nil, fmt.Errorf("%v is not in scope", i)
+	}
+	return v, nil
+}
+
+func (s *Scope) Set(k, v Func) (Func, error) { // nolint
+	return s.Add(ID(k.(String)), v), nil
 }
 
 func (s *Scope) String() string { // nolint
@@ -864,10 +871,10 @@ func AssignPattern(frame Frame, scope *Scope, ids []ID, val Func) (*Scope, Func)
 	}) (*Scope, Func) {
 		m := make(map[ID]Func, len(ids))
 		for i, id := range ids {
-			v, ok := f.At(Number(i))
-			if !ok {
+			v, err := f.At(Number(i))
+			if err != nil {
 				return nil, &Error{
-					Err:   errors.New("Atter shorter than pattern"),
+					Err:   err,
 					Frame: frame,
 				}
 			}

wdte_test.go

@@ -442,6 +442,16 @@ func TestStd(t *testing.T) {
 			script: `let m => import 'math'; at m 'pi';`,
 			ret:    wdte.Number(math.Pi),
 		},
+		{
+			name:   "Set/Scope",
+			script: `let t => collect (let test => 3); let t => set t 'test2' 5; t.test2;`,
+			ret:    wdte.Number(5),
+		},
+		{
+			name:   "Set/Array",
+			script: `let t => [1; 2; 3]; set t 1 5;`,
+			ret:    wdte.Array{wdte.Number(1), wdte.Number(5), wdte.Number(3)},
+		},
 		{
 			name:   "Collect",
 			script: `let t => collect (let test => 3); t.test;`,
@@ -452,11 +462,6 @@ func TestStd(t *testing.T) {
 			script: `let t => collect (let test => 3; let other => 5); known t;`,
 			ret:    wdte.Array{wdte.String("other"), wdte.String("test")},
 		},
-		{
-			name:   "Sub",
-			script: `let t => collect (let test => 3); let t => sub t 'test2' 5; t.test2;`,
-			ret:    wdte.Number(5),
-		},
 		{
 			name:   "Reflect",
 			script: `[reflect 'string' 'String'; 'string' {reflect 'String' => 'test'}];`,