Parser & desugarer support for "in"

ast/ast.go

@@ -162,6 +162,7 @@ const (
 	BopGreaterEq
 	BopLess
 	BopLessEq
+	BopIn
 
 	BopManifestEqual
 	BopManifestUnequal
@@ -189,6 +190,7 @@ var bopStrings = []string{
 	BopGreaterEq: ">=",
 	BopLess:      "<",
 	BopLessEq:    "<=",
+	BopIn:        "in",
 
 	BopManifestEqual:   "==",
 	BopManifestUnequal: "!=",
@@ -216,6 +218,7 @@ var BopMap = map[string]BinaryOp{
 	">=": BopGreaterEq,
 	"<":  BopLess,
 	"<=": BopLessEq,
+	"in": BopIn,
 
 	"==": BopManifestEqual,
 	"!=": BopManifestUnequal,
@@ -496,6 +499,12 @@ type SuperIndex struct {
 	Id    *Identifier
 }
 
+// Represents the e in super construct.
+type InSuper struct {
+	NodeBase
+	Index Node
+}
+
 // ---------------------------------------------------------------------------
 
 type UnaryOp int

desugarer.go

@@ -509,6 +509,11 @@ func desugar(astPtr *ast.Node, objLevel int) (err error) {
 			node.Id = nil
 		}
 
+	case *ast.InSuper:
+		err := desugar(&node.Index, objLevel)
+		if err != nil {
+			return err
+		}
 	case *ast.Unary:
 		err = desugar(&node.Expr, objLevel)
 		if err != nil {

parser/parser.go

@@ -43,6 +43,7 @@ var bopPrecedence = map[ast.BinaryOp]precedence{
 	ast.BopGreaterEq:       8,
 	ast.BopLess:            8,
 	ast.BopLessEq:          8,
+	ast.BopIn:              8,
 	ast.BopManifestEqual:   9,
 	ast.BopManifestUnequal: 9,
 	ast.BopBitwiseAnd:      10,
@@ -940,6 +941,11 @@ func (p *parser) parse(prec precedence) (ast.Node, error) {
 			// with higher precedence, then return lhs and let lower levels deal with
 			// the operator.
 			switch p.peek().kind {
+			case tokenIn:
+				bop = ast.BopIn
+				if bopPrecedence[bop] != prec {
+					return lhs, nil
+				}
 			case tokenOperator:
 				_ = "breakpoint"
 				if p.peek().data == ":" {
@@ -1069,15 +1075,23 @@ func (p *parser) parse(prec precedence) (ast.Node, error) {
 					Right:    obj,
 				}
 			default:
-				rhs, err := p.parse(prec - 1)
-				if err != nil {
-					return nil, err
-				}
-				lhs = &ast.Binary{
-					NodeBase: ast.NewNodeBaseLoc(locFromTokenAST(begin, rhs)),
-					Left:     lhs,
-					Op:       bop,
-					Right:    rhs,
+				if op.kind == tokenIn && p.peek().kind == tokenSuper {
+					super := p.pop()
+					lhs = &ast.InSuper{
+						NodeBase: ast.NewNodeBaseLoc(locFromTokens(begin, super)),
+						Index:    lhs,
+					}
+				} else {
+					rhs, err := p.parse(prec - 1)
+					if err != nil {
+						return nil, err
+					}
+					lhs = &ast.Binary{
+						NodeBase: ast.NewNodeBaseLoc(locFromTokenAST(begin, rhs)),
+						Left:     lhs,
+						Op:       bop,
+						Right:    rhs,
+					}
 				}
 			}
 		}

parser/parser_test.go

@@ -107,6 +107,9 @@ var tests = []string{
 	`[][:1:1]`,
 	`[][1::1]`,
 	`[][1:1:1]`,
+
+	`a in b`,
+	`{ x: if "opt" in super then "x" else "y" }`,
 }
 
 func TestParser(t *testing.T) {