From 0163d0b76415907e1558065560d738d0b66a167b Mon Sep 17 00:00:00 2001
From: Ryu <114303361+ryuapp@users.noreply.github.com>
Date: Wed, 11 Mar 2026 00:51:42 +0900
Subject: [PATCH] feat: add `%` (modulo) operator

---
 src/codegen/zig/mod.rs                        |  6 ++++--
 src/lexer.rs                                  |  5 +++++
 src/parser.rs                                 |  2 ++
 src/tests/codegen.rs                          | 12 +++++++++++
 src/tests/fixtures/modulo.zy                  |  3 +++
 ...napshots__codegen_snapshots@modulo.zy.snap |  9 ++++++++
 src/tests/typechecker.rs                      | 21 +++++++++++++++++++
 src/typechecker.rs                            |  2 +-
 8 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 src/tests/fixtures/modulo.zy
 create mode 100644 src/tests/snapshots/zyre__tests__snapshots__codegen_snapshots@modulo.zy.snap

diff --git a/src/codegen/zig/mod.rs b/src/codegen/zig/mod.rs
index e2ab57d..53cca07 100644
--- a/src/codegen/zig/mod.rs
+++ b/src/codegen/zig/mod.rs
@@ -520,7 +520,11 @@ impl ZigBackend {
             }
 
             ExprKind::BinOp { op, lhs, rhs } => {
+                let lhs_s = self.gen_expr(lhs);
+                let rhs_s = self.gen_expr(rhs);
                 let op_str = match op {
+                    // Zig requires @rem for signed integer remainder (% only works on unsigned)
+                    BinOp::Mod => return format!("@rem({}, {})", lhs_s, rhs_s),
                     BinOp::Add => "+",
                     BinOp::Sub => "-",
                     BinOp::Mul => "*",
@@ -534,8 +538,6 @@ impl ZigBackend {
                     BinOp::And => "and",
                     BinOp::Or => "or",
                 };
-                let lhs_s = self.gen_expr(lhs);
-                let rhs_s = self.gen_expr(rhs);
                 format!("({} {} {})", lhs_s, op_str, rhs_s)
             }
 
diff --git a/src/lexer.rs b/src/lexer.rs
index 2f58850..0d42c0c 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -36,6 +36,7 @@ pub enum Token {
     Minus,    // -
     Star,     // *
     Slash,    // /
+    Percent,  // %
     And,      // &&
     Or,       // ||
     Bang,     // !
@@ -204,6 +205,10 @@ fn tokenize_raw(source: &str) -> Vec<(Token, Span)> {
                 chars.next();
                 tokens.push((Token::Star, (pos, end_pos!())));
             }
+            '%' => {
+                chars.next();
+                tokens.push((Token::Percent, (pos, end_pos!())));
+            }
             '.' => {
                 chars.next();
                 tokens.push((Token::Dot, (pos, end_pos!())));
diff --git a/src/parser.rs b/src/parser.rs
index b849d7e..f571c7f 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -96,6 +96,7 @@ pub enum BinOp {
     Sub,
     Mul,
     Div,
+    Mod,
     Eq,
     NotEq,
     Lt,
@@ -706,6 +707,7 @@ impl Parser {
             let op = match self.peek() {
                 Token::Star => BinOp::Mul,
                 Token::Slash => BinOp::Div,
+                Token::Percent => BinOp::Mod,
                 _ => break,
             };
             self.advance();
diff --git a/src/tests/codegen.rs b/src/tests/codegen.rs
index 8b021df..ee6c2e0 100644
--- a/src/tests/codegen.rs
+++ b/src/tests/codegen.rs
@@ -281,3 +281,15 @@ fn test_codegen_export_const_hoisted() {
     let main_start = out.find("pub fn main").unwrap_or(out.len());
     assert!(!out[main_start..].contains("const c ="), "got:\n{}", out);
 }
+
+#[test]
+fn test_codegen_modulo() {
+    let out = compile(
+        r#"
+        export fn rem(a: i32, b: i32): i32 {
+            return a % b;
+        }
+    "#,
+    );
+    assert!(out.contains("@rem(a, b)"), "got:\n{}", out);
+}
diff --git a/src/tests/fixtures/modulo.zy b/src/tests/fixtures/modulo.zy
new file mode 100644
index 0000000..e768797
--- /dev/null
+++ b/src/tests/fixtures/modulo.zy
@@ -0,0 +1,3 @@
+export fn rem(a: i32, b: i32): i32 {
+    return a % b;
+}
diff --git a/src/tests/snapshots/zyre__tests__snapshots__codegen_snapshots@modulo.zy.snap b/src/tests/snapshots/zyre__tests__snapshots__codegen_snapshots@modulo.zy.snap
new file mode 100644
index 0000000..0345f07
--- /dev/null
+++ b/src/tests/snapshots/zyre__tests__snapshots__codegen_snapshots@modulo.zy.snap
@@ -0,0 +1,9 @@
+---
+source: src/tests/snapshots.rs
+assertion_line: 10
+expression: output
+input_file: src/tests/fixtures/modulo.zy
+---
+pub fn rem(a: i32, b: i32) i32 {
+    return @rem(a, b);
+}
diff --git a/src/tests/typechecker.rs b/src/tests/typechecker.rs
index 476124a..e5a154b 100644
--- a/src/tests/typechecker.rs
+++ b/src/tests/typechecker.rs
@@ -257,3 +257,24 @@ fn test_if_expr_branch_type_mismatch() {
         "if branches have different types",
     );
 }
+
+#[test]
+fn test_modulo_ok() {
+    ok(r#"
+        export fn rem(a: i32, b: i32): i32 { return a % b; }
+    "#);
+}
+
+#[test]
+fn test_modulo_type_mismatch() {
+    err(
+        r#"
+        fn main(): void {
+            const x: i32 = 10;
+            const y: f64 = 3.0;
+            const _z = x % y;
+        }
+    "#,
+        "Binary op type mismatch",
+    );
+}
diff --git a/src/typechecker.rs b/src/typechecker.rs
index 6b9dff9..aa31f22 100644
--- a/src/typechecker.rs
+++ b/src/typechecker.rs
@@ -609,7 +609,7 @@ impl TypeChecker {
                 let lhs_ty = self.check_expr(lhs, scope);
                 let rhs_ty = self.check_expr(rhs, scope);
                 match op {
-                    BinOp::Add | BinOp::Sub | BinOp::Mul | BinOp::Div => {
+                    BinOp::Add | BinOp::Sub | BinOp::Mul | BinOp::Div | BinOp::Mod => {
                         if lhs_ty != rhs_ty {
                             self.error(format!(
                                 "Binary op type mismatch: '{}' vs '{}'",