instantiate variables in numerical comparisons

src/prolog/codegen.rs

@@ -304,6 +304,14 @@ impl<'a, TermMarker: Allocator<'a>> CodeGenerator<TermMarker>
     {
         match ct {
             &InlinedClauseType::CompareNumber(cmp, ..) => {
+                if let &Term::Var(ref vr, ref name) = terms[0].as_ref() {
+                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code);                    
+                }
+
+                if let &Term::Var(ref vr, ref name) = terms[1].as_ref() {
+                    self.mark_non_callable(name.clone(), 2, term_loc, vr, code);                    
+                }
+                
                 let (mut lcode, at_1) = self.call_arith_eval(terms[0].as_ref(), 1)?;
                 let (mut rcode, at_2) = self.call_arith_eval(terms[1].as_ref(), 2)?;
 

src/prolog/machine/machine_errors.rs

@@ -251,7 +251,7 @@ pub enum EvalError {
 //    FloatOverflow,
 //    IntOverflow,
 //    Undefined,
-//    Underflow,
+//    FloatUnderflow,
     ZeroDivisor,
     NoRoots
 }
@@ -262,7 +262,7 @@ impl EvalError {
 //            EvalError::FloatOverflow => "float_overflow",
 //            EvalError::IntOverflow => "int_overflow",
 //            EvalError::Undefined => "undefined",
-//            EvalError::Underflow => "underflow",
+//            EvalError::FloatUnderflow => "underflow",
             EvalError::ZeroDivisor => "zero_divisor",
             EvalError::NoRoots => "no_roots"
         }