Add slice index syntax to grammar

parser/cst/nodes.go

@@ -40,6 +40,10 @@ type (
 		QualifiedIdent QualifiedIdent
 		Args           []any
 	}
+	IndexExpr struct {
+		BaseExpr  any
+		IndexExpr any
+	}
 	SliceType struct {
 		Type any
 	}
@@ -84,6 +88,14 @@ type (
 	}
 )
 
+func MakeIndexExpr(baseExpr, indexExpr any) (IndexExpr, error) {
+	result := IndexExpr{
+		BaseExpr:  baseExpr,
+		IndexExpr: indexExpr,
+	}
+	return result, nil
+}
+
 func AppendToParamSlice(slice, item any) ([]Param, error) {
 	s := slice.([]Param)
 	i := item.(Param)

parser/expr_test.go

@@ -47,6 +47,40 @@ func Test_BinOp(t *testing.T) {
 	testStmts(t, tcs)
 }
 
+func Test_IndexExpr(t *testing.T) {
+
+	tcs := []TestForStmt{
+		{
+			Name:  "identifier indexed with uint literal",
+			Input: `a[1];`,
+			Output: cst.IndexExpr{
+				BaseExpr:  cst.QualifiedIdent{Ident: "a"},
+				IndexExpr: cst.UintLit{Value: 1},
+			},
+		},
+		{
+			Name:  "identifier indexed with identifier",
+			Input: `a[i];`,
+			Output: cst.IndexExpr{
+				BaseExpr:  cst.QualifiedIdent{Ident: "a"},
+				IndexExpr: cst.QualifiedIdent{Ident: "i"},
+			},
+		},
+		{
+			Name:  "function call indexed with uint literal",
+			Input: `f()[1];`,
+			Output: cst.IndexExpr{
+				BaseExpr: cst.Call{
+					QualifiedIdent: cst.QualifiedIdent{Ident: "f"},
+				},
+				IndexExpr: cst.UintLit{Value: 1},
+			},
+		},
+	}
+
+	testStmts(t, tcs)
+}
+
 func Test_IntLit(t *testing.T) {
 
 	tcs := []TestForStmt{

parser/grammar.bnf

@@ -140,15 +140,19 @@ Expr5
 | PrimaryExpr    << $0, nil >>
 ;
 
-PrimaryExpr
-: Operand       << $0, nil >>
 // TODO: // https://go.dev/ref/spec#PrimaryExpr
 // | Conversion
-// | PrimaryExpr Index
 // | PrimaryExpr Slice
+PrimaryExpr
+: Operand       << $0, nil >>
+| PrimaryExpr Index << cst.MakeIndexExpr($0, $1) >>
 | PrimaryExpr Arguments  << cst.MakeCall($0, $1) >>
 ;
 
+Index
+: "[" Expr1 "]"   << $1, nil >>
+;
+
 Arguments
 : "(" ")"                   << nil, nil >>
 | "(" ExpressionList ")"    << $1, nil >>