Make anchor arg parsing robust to recent changes

carcara/src/parser/mod.rs

@@ -984,8 +984,21 @@ impl<'a, R: BufRead> Parser<'a, R> {
         self.expect_token(Token::OpenParen)?;
         Ok(if self.current_token == Token::Keyword("=".into()) {
             self.next_token()?;
-            let (var, sort) = self.parse_sorted_var()?;
-            let value = self.parse_term_expecting_sort(sort.as_sort().unwrap())?;
+
+            // To make Carcara more robust to recent changes in the Alethe format, we support
+            // parsing the two versions of assign-style anchor arguments:
+            // - the old version, without the sort hint: `(:= <symbol> <term>)`
+            // - and the new version, with the sort hint: `(:= (<symbol> <sort>) <term>)`
+            let (var, value, sort) = if matches!(self.current_token, Token::Symbol(_)) {
+                let var = self.expect_symbol()?;
+                let value = self.parse_term()?;
+                let sort = self.pool.sort(&value);
+                (var, value, sort)
+            } else {
+                let (var, sort) = self.parse_sorted_var()?;
+                let value = self.parse_term_expecting_sort(sort.as_sort().unwrap())?;
+                (var, value, sort)
+            };
             self.insert_sorted_var((var.clone(), sort.clone()));
             self.expect_token(Token::CloseParen)?;
             AnchorArg::Assign((var, sort), value)