From 819826627f90aecdd1d91e24563fe2162061ccf2 Mon Sep 17 00:00:00 2001
From: Marc Vertes <mvertes@free.fr>
Date: Sat, 4 Nov 2023 17:56:15 +0100
Subject: fix: skip parsing empty expression

---
 parser/README.md           | 2 +-
 parser/expr.go             | 4 ++--
 parser/interpreter_test.go | 4 ++--
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/parser/README.md b/parser/README.md
index 23c23b8..c9ff440 100644
--- a/parser/README.md
+++ b/parser/README.md
@@ -70,7 +70,7 @@ Go language support:
 - [ ] select statement
 - [x] binary operators
 - [ ] unary operators
-- [ ] logical operators && and ||
+- [x] logical operators && and ||
 - [ ] assign operators
 - [x] operator precedence rules
 - [x] parenthesis expressions
diff --git a/parser/expr.go b/parser/expr.go
index 18c97a5..d626e9e 100644
--- a/parser/expr.go
+++ b/parser/expr.go
@@ -85,7 +85,7 @@ func (p *Parser) ParseExpr(in Tokens) (out Tokens, err error) {
 	if out, err = p.ParseLogical(out); err != nil {
 		return out, err
 	}
-	if l := len(out) - 1; out[l].Id == lang.Define || out[l].Id == lang.Assign {
+	if l := len(out) - 1; l >= 0 && (out[l].Id == lang.Define || out[l].Id == lang.Assign) {
 		// Handle the assignment of a logical expression.
 		s1 := p.subExprLen(out[:l])
 		head, err := p.ParseLogical(out[:l-s1])
@@ -139,7 +139,7 @@ func (p *Parser) ParseExprStr(s string) (tokens Tokens, err error) {
 // If the last token is not a logical operator then the function is idempotent.
 func (p *Parser) ParseLogical(in Tokens) (out Tokens, err error) {
 	l := len(in) - 1
-	if !in[l].Id.IsLogicalOp() {
+	if l < 0 || !in[l].Id.IsLogicalOp() {
 		return in, nil
 	}
 	xp := strconv.Itoa(p.labelCount[p.scope])
diff --git a/parser/interpreter_test.go b/parser/interpreter_test.go
index 9794337..02cd105 100644
--- a/parser/interpreter_test.go
+++ b/parser/interpreter_test.go
@@ -96,8 +96,8 @@ func TestIf(t *testing.T) {
 		{src: "a := 0; if a == 1 { a = 2 } else { a = 1 }; a", res: "1"},
 		{src: "a := 0; if a == 1 { a = 2 } else if a == 0 { a = 3 } else { a = 1 }; a", res: "3"},
 		{src: "a := 0; if a == 1 { a = 2 } else if a == 2 { a = 3 } else { a = 1 }; a", res: "1"},
-		//{src: "a := 1; if a > 0 && a < 2 { a = 3 }; a", res: "3"},
-		//{src: "a := 1; if a < 0 || a < 2 { a = 3 }; a", res: "3"},
+		{src: "a := 1; if a > 0 && a < 2 { a = 3 }; a", res: "3"},
+		{src: "a := 1; if a < 0 || a < 2 { a = 3 }; a", res: "3"},
 	})
 }
 
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