Fixes https://github.com/cozodb/cozo/issues/99

cozo-core/src/data/functions.rs

@@ -1069,6 +1069,9 @@ define_op!(OP_MOD, 2, false);
 pub(crate) fn op_mod(args: &[DataValue]) -> Result<DataValue> {
     Ok(match (&args[0], &args[1]) {
         (DataValue::Num(Num::Int(a)), DataValue::Num(Num::Int(b))) => {
+            if *b == 0 {
+                bail!("'mod' requires non-zero divisor")
+            }
             DataValue::Num(Num::Int(a.rem(b)))
         }
         (DataValue::Num(Num::Float(a)), DataValue::Num(Num::Float(b))) => {

cozo-core/src/data/tests/functions.rs

@@ -80,6 +80,7 @@ fn test_div() {
         op_div(&[DataValue::from(7.0), DataValue::from(0.5)]).unwrap(),
         DataValue::from(14.0)
     );
+    assert!(op_div(&[DataValue::from(1), DataValue::from(0)]).is_ok());
 }
 
 #[test]
@@ -538,6 +539,10 @@ fn test_mod() {
         op_mod(&[DataValue::from(-10), DataValue::from(7)]).unwrap(),
         DataValue::from(-3)
     );
+    assert!(op_mod(&[DataValue::from(5), DataValue::from(0.)]).is_ok());
+    assert!(op_mod(&[DataValue::from(5.), DataValue::from(0.)]).is_ok());
+    assert!(op_mod(&[DataValue::from(5.), DataValue::from(0)]).is_ok());
+    assert!(op_mod(&[DataValue::from(5), DataValue::from(0)]).is_err());
 }
 
 #[test]