feat(tvix/eval): Support builtins.lessThan r/4955

Extend and export the `cmp_op`, and this becomes trivial.

Change-Id: I9c93fa4db0f5a1fc8b56928ea144676f79247de1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6557
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

1 files changed, 20 insertions, 13 deletions

diff --git a/tvix/eval/src/vm.rs b/tvix/eval/src/vm.rs
index 87adfe5611..52627a1fea 100644
--- a/tvix/eval/src/vm.rs
+++ b/tvix/eval/src/vm.rs
@@ -94,29 +94,36 @@ macro_rules! arithmetic_op {
     }};
 }
 
+#[macro_export]
 macro_rules! cmp_op {
     ( $self:ident, $op:tt ) => {{
         let b = $self.pop();
         let a = $self.pop();
+        let result = fallible!($self, cmp_op!(&a, &b, $op));
+        $self.push(result);
+    }};
 
+    ( $a:expr, $b:expr, $op:tt ) => {
         // Comparable (in terms of ordering) values are numbers and
         // strings. Numbers need to be coerced similarly to arithmetic
         // ops if mixed types are encountered.
-        let result = match (a, b) {
-            (Value::Integer(i1), Value::Integer(i2)) => i1 $op i2,
-            (Value::Float(f1), Value::Float(f2)) => f1 $op f2,
-            (Value::Integer(i1), Value::Float(f2)) => (i1 as f64) $op f2,
-            (Value::Float(f1), Value::Integer(i2)) => f1 $op (i2 as f64),
-            (Value::String(s1), Value::String(s2)) => s1 $op s2,
-
-            (lhs, rhs) => return Err($self.error(ErrorKind::Incomparable {
+        match ($a, $b) {
+            // same types
+            (Value::Integer(i1), Value::Integer(i2)) => Ok(Value::Bool(i1 $op i2)),
+            (Value::Float(f1), Value::Float(f2)) => Ok(Value::Bool(f1 $op f2)),
+            (Value::String(s1), Value::String(s2)) => Ok(Value::Bool(s1 $op s2)),
+
+            // different types
+            (Value::Integer(i1), Value::Float(f2)) => Ok(Value::Bool((*i1 as f64) $op *f2)),
+            (Value::Float(f1), Value::Integer(i2)) => Ok(Value::Bool(*f1 $op (*i2 as f64))),
+
+            // unsupported types
+            (lhs, rhs) => Err(ErrorKind::Incomparable {
                 lhs: lhs.type_of(),
                 rhs: rhs.type_of(),
-            })),
-        };
-
-        $self.push(Value::Bool(result));
-    }};
+            }),
+        }
+    }
 }
 
 impl<'o> VM<'o> {