add error checking file oops

tree_shared/src/error_checking.rs

@@ -0,0 +1,58 @@
+//! Rules that perform sanity checks,
+//! such as checking that switch children
+//! are all `Branch`es.
+
+use strum::IntoEnumIterator;
+
+use crate::ir::{Constructor, ESort};
+
+pub(crate) fn error_checking_rules() -> Vec<String> {
+    let mut res = vec![format!(
+        "
+(relation IsBranchList (ListExpr))
+
+(rule ((Switch pred outputs))
+      ((IsBranchList outputs))
+      :ruleset error-checking)
+
+(rule ((IsBranchList (Cons a rest)))
+      ((IsBranchList rest))
+      :ruleset error-checking)
+  "
+    )];
+
+    for ctor in Constructor::iter() {
+        if ctor.sort() == ESort::ListExpr {
+            continue;
+        }
+        if ctor == Constructor::Branch {
+            continue;
+        }
+
+        let pat = ctor.construct(|field| field.var());
+        res.push(format!(
+            "
+(rule ((IsBranchList (Cons {pat} rest)))
+      ((panic \"Expected Branch, got {ctor}\"))
+      :ruleset error-checking)
+"
+        ));
+    }
+
+    res
+}
+
+#[test]
+#[should_panic(expected = "Expected Branch, got Num")]
+fn test_switch_with_num_child() {
+    let build = "
+    (Switch
+        (Num (Shared) 0)
+        (Cons
+            (Num (Shared) 1)
+            (Cons
+                (Branch (Shared) (Num (Shared) 2))
+                (Nil))))
+    ";
+    crate::run_test(build, "").unwrap()
+}