Handle input predicates correctly

src/ast.rs

@@ -117,7 +117,8 @@ impl PredicateDeclaration
 		let dependencies = match *dependencies
 		{
 			Some(ref dependencies) => dependencies,
-			None => unreachable!("all dependencies should have been collected at this point"),
+			// Input predicates don’t have completed definitions and no dependencies, so ignore them
+			None => return,
 		};
 
 		for dependency in dependencies.iter()

src/problem.rs

@@ -69,6 +69,11 @@ impl Problem
 				continue;
 			}
 
+			if *predicate_declaration.is_input.borrow()
+			{
+				continue;
+			}
+
 			let matching_statement = |statement: &&Statement|
 				match statement.kind
 				{