wdte: Add rev and method (#198)

* wdte: Remove `Func` from `Assigner`.

* res/grammar: Add `rev` and `method` funcmods.

* scanner: Add `rev` and `method` keywords.

* wdte: Refactor function creation into a shared function.

* wdte: Implement `rev` and `method`.

* wdte: Don't use 'fmt.Sprint()' to write to a `strings.Builder`.

Huh. What in the world.

res/grammar.ebnf

@@ -2,6 +2,8 @@
   <funcmods> -> <funcmod> <funcmods>
               | ε
    <funcmod> -> memo
+              | rev
+              | method
   <argdecls> -> <argdecl> <argdecls>
               | ε
    <argdecl> -> id

scanner/util.go

@@ -27,6 +27,8 @@ var (
 
 	keywords = []string{
 		"memo",
+		"rev",
+		"method",
 		"let",
 		"import",
 	}

translate.go

@@ -49,6 +49,12 @@ func (m *translator) fromFuncMod(funcMod *ast.NTerm) funcMod {
 	case "memo":
 		return funcModMemo
 
+	case "rev":
+		return funcModRev
+
+	case "method":
+		return funcModMethod
+
 	default:
 		panic(fmt.Errorf("Malformed AST with bad <funcmod>: %v", mod))
 	}
@@ -121,25 +127,9 @@ func (m *translator) fromLetExpr(expr *ast.NTerm) Func {
 			argIDs = append(argIDs, arg.IDs()...)
 		}
 
-		if mods&funcModMemo != 0 {
-			inner = &Memo{
-				Func: inner,
-				Args: argIDs,
-			}
-		}
-
-		right := inner
-		if len(args) > 0 {
-			right = &Lambda{
-				ID:   id,
-				Expr: inner,
-				Args: args,
-			}
-		}
-
 		return &LetAssigner{
 			Assigner: SimpleAssigner(id),
-			Expr:     right,
+			Expr:     m.fromFuncDecl(mods, id, args, inner),
 		}
 
 	case "argdecl":
@@ -283,6 +273,47 @@ func (m *translator) fromCompound(compound *ast.NTerm) Func {
 	return r
 }
 
+func (m *translator) fromFuncDecl(mods funcMod, id ID, args []Assigner, expr Func) Func {
+	if (mods == 0) && (len(args) == 0) {
+		return expr
+	}
+
+	if mods&funcModMemo != 0 {
+		argIDs := make([]ID, 0, len(args))
+		for _, arg := range args {
+			argIDs = append(argIDs, arg.IDs()...)
+		}
+
+		expr = &Memo{
+			Func: expr,
+			Args: argIDs,
+		}
+	}
+
+	argSplit := func(assigners []Assigner, args []Func) ([]Assigner, []Assigner) {
+		return assigners[:len(args)], assigners[len(args):]
+	}
+	if mods&funcModRev != 0 {
+		argSplit = func(assigners []Assigner, args []Func) ([]Assigner, []Assigner) {
+			return assigners[len(assigners)-len(args):], assigners[:len(assigners)-len(args)]
+		}
+	}
+
+	var method Assigner
+	if mods&funcModMethod != 0 {
+		method = args[0]
+		args = args[1:]
+	}
+
+	return &Lambda{
+		ID:       id,
+		Expr:     expr,
+		Args:     args,
+		ArgSplit: argSplit,
+		Method:   method,
+	}
+}
+
 func (m *translator) fromLambda(lambda *ast.NTerm) (f Func) {
 	mods := m.fromFuncMods(lambda.Children()[1].(*ast.NTerm))
 	id := ID(lambda.Children()[2].(*ast.Term).Tok().Val.(string))
@@ -296,23 +327,7 @@ func (m *translator) fromLambda(lambda *ast.NTerm) (f Func) {
 		}
 	}
 
-	argIDs := make([]ID, 0, len(args))
-	for _, arg := range args {
-		argIDs = append(argIDs, arg.IDs()...)
-	}
-
-	if mods&funcModMemo != 0 {
-		inner = &Memo{
-			Func: inner,
-			Args: argIDs,
-		}
-	}
-
-	return &Lambda{
-		ID:   id,
-		Expr: inner,
-		Args: args,
-	}
+	return m.fromFuncDecl(mods, id, args, inner)
 }
 
 func (m *translator) fromImport(im *ast.NTerm) Func {
@@ -380,4 +395,6 @@ type funcMod uint
 
 const (
 	funcModMemo funcMod = 1 << iota
+	funcModRev
+	funcModMethod
 )

wdte.go

@@ -580,7 +580,7 @@ func (c Compound) Collect(frame Frame) (letScope *Scope, last Func) {
 	for _, f := range c {
 		switch f := f.(type) {
 		case Assigner:
-			letScope, last = f.Assign(frame, letScope, f)
+			letScope, last = f.Assign(frame, letScope, last)
 		default:
 			last = f.Call(frame.WithScope(frame.Scope().Sub(letScope)))
 		}
@@ -735,44 +735,65 @@ func (cache *memoCache) Set(args []Func, val Func) {
 // and its first and second arguments under the IDs "x" and "y",
 // respectively. It will then evaluate `+ x y` in that new scope.
 type Lambda struct {
-	ID   ID
-	Expr Func
-	Args []Assigner
+	ID       ID
+	Expr     Func
+	Args     []Assigner
+	ArgSplit func([]Assigner, []Func) ([]Assigner, []Assigner)
+	Method   Assigner
 
 	Scope    *Scope
 	Original *Lambda
 }
 
+func (lambda *Lambda) original() *Lambda {
+	if lambda.Original == nil {
+		return lambda
+	}
+
+	return lambda.Original
+}
+
 func (lambda *Lambda) Call(frame Frame, args ...Func) Func { // nolint
 	scope := lambda.Scope
 	if scope == nil {
 		scope = frame.Scope()
 	}
 
-	original := lambda.Original
-	if original == nil {
-		original = lambda
-	}
-
 	if len(args) < len(lambda.Args) {
+		assigners, rem := lambda.ArgSplit(lambda.Args, args)
 		for i := range args {
-			scope, _ = lambda.Args[i].Assign(frame, scope, args[i])
+			scope, _ = assigners[i].Assign(frame, scope, args[i])
 		}
 
 		return &Lambda{
-			ID:   lambda.ID,
-			Expr: lambda.Expr,
-			Args: lambda.Args[len(args):],
+			ID:       lambda.ID,
+			Expr:     lambda.Expr,
+			Args:     rem,
+			ArgSplit: lambda.ArgSplit,
+			Method:   lambda.Method,
 
 			Scope:    scope,
-			Original: original,
+			Original: lambda.original(),
 		}
 	}
 
 	for i := range lambda.Args {
 		scope, _ = lambda.Args[i].Assign(frame, scope, args[i])
 	}
 
+	if lambda.Method != nil {
+		return &Lambda{
+			ID:       lambda.ID,
+			Expr:     lambda.Expr,
+			Args:     []Assigner{lambda.Method},
+			ArgSplit: lambda.ArgSplit,
+
+			Scope:    scope,
+			Original: lambda.original(),
+		}
+	}
+
+	original := lambda.original()
 	scope = scope.Add(original.ID, original)
 	return lambda.Expr.Call(frame.WithScope(scope))
 }
@@ -791,10 +812,9 @@ func (lambda *Lambda) String() string { // nolint
 }
 
 // An Assigner places items into a scope. How exactly iy does this
-// differs, but the general idea is to produce a subscope from a combination of frame, an existing scope, and a function.
+// differs, but the general idea is to produce a subscope from a
+// combination of frame, an existing scope, and a function.
 type Assigner interface {
-	Func
-
 	// Assign produces a subscope from an existing frame, scope, and
 	// function, returning both the new subscope and a function. The
 	// returned function may or may not be related to the original
@@ -815,10 +835,6 @@ type Assigner interface {
 // value.
 type SimpleAssigner ID
 
-func (a SimpleAssigner) Call(frame Frame, args ...Func) Func {
-	return a
-}
-
 func (a SimpleAssigner) Assign(frame Frame, scope *Scope, val Func) (*Scope, Func) {
 	frame = frame.WithScope(frame.Scope().Sub(scope))
 
@@ -855,10 +871,6 @@ func (a SimpleAssigner) String() string {
 //    c = 3
 type PatternAssigner []Assigner
 
-func (a PatternAssigner) Call(frame Frame, args ...Func) Func {
-	return a
-}
-
 func (a PatternAssigner) Assign(frame Frame, scope *Scope, val Func) (*Scope, Func) {
 	assignAtter := func(frame Frame, f interface {
 		Func
@@ -926,7 +938,7 @@ func (a PatternAssigner) String() string {
 	sep := ""
 	for _, a := range a {
 		buf.WriteString(sep)
-		buf.WriteString(fmt.Sprint(a))
+		fmt.Fprint(&buf, a)
 
 		sep = " "
 	}

wdte_test.go

@@ -220,6 +220,21 @@ func TestBasics(t *testing.T) {
 			script: `let memo test [a [b]] c => + a b c; (test [1; [2]] 3; test [1; [2]] 3);`,
 			ret:    wdte.Number(6),
 		},
+		{
+			name:   "Simple/Rev",
+			script: `let rev test a b c => [a; b; c]; (test 1 2) 3;`,
+			ret:    wdte.Array{wdte.Number(3), wdte.Number(1), wdte.Number(2)},
+		},
+		{
+			name:   "Simple/Method",
+			script: `let method test r a b => [r; a; b]; 3 -> test 1 2;`,
+			ret:    wdte.Array{wdte.Number(3), wdte.Number(1), wdte.Number(2)},
+		},
+		{
+			name:   "Simple/RevMethod",
+			script: `let method rev test r a b c => [r; a; b; c]; 0 -> (test 1 2) 3;`,
+			ret:    wdte.Array{wdte.Number(0), wdte.Number(3), wdte.Number(1), wdte.Number(2)},
+		},
 		{
 			name:   "Simple/VariableArgs",
 			script: `let test => +; test 3 5;`,