Broken structure now gets through syntax evaluator.

src/eval.rs

@@ -86,6 +86,14 @@ pub enum EvalError<IR> {
         usize,
         usize,
     ),
+    #[error("Value has no fields {1} (attempt to get field {2} at {0:?})")]
+    NoFieldForValue(crate::syntax::Location, Value<IR>, ArcIntern<String>),
+    #[error("Bad field {2} for structure {1:?} at {0:?}")]
+    BadFieldForStructure(
+        crate::syntax::Location,
+        Option<ArcIntern<String>>,
+        ArcIntern<String>,
+    ),
 }
 
 impl<IR1: Clone, IR2: Clone> PartialEq<EvalError<IR1>> for EvalError<IR2> {
@@ -149,6 +157,16 @@ impl<IR1: Clone, IR2: Clone> PartialEq<EvalError<IR1>> for EvalError<IR2> {
                 EvalError::WrongArgCount(w, x, y, z) => a == w && b == x && c == y && d == z,
                 _ => false,
             },
+
+            EvalError::NoFieldForValue(a, b, c) => match other {
+                EvalError::NoFieldForValue(x, y, z) => a == x && b == y && c == z,
+                _ => false,
+            },
+
+            EvalError::BadFieldForStructure(a, b, c) => match other {
+                EvalError::BadFieldForStructure(x, y, z) => a == x && b == y && c == z,
+                _ => false,
+            },
         }
     }
 }