Fixed bug of degree insensitivity in polynomial addition

Summary: As title.

Reviewed By: grievejia

Differential Revision: D28890244

fbshipit-source-id: 28a9f04ec80293ec4ebf4b3846812fd1ea981e08

Author: Brandon Wu

source/analysis/test/typeTest.ml

@@ -3150,7 +3150,7 @@ let test_polynomial_create_from_list _ =
     [
       2, [y, 1]; 1, [x, 1]; 1, [x, 2; y, 1]; 1, [z, 1]; 1, [y, 1; z, 1; x, 1]; 1, [x, 1; y, 2]; 2, [];
     ]
-    "2 + x + 2y + z + x^2y + xy^2 + xyz";
+    "2 + x + 2y + z + xyz + xy^2 + x^2y";
   ()
 
 
@@ -3270,6 +3270,7 @@ let test_add_polynomials _ =
   assert_add [3, []] [2, []] "5";
   assert_add [3, []] [-3, []; 2, [x, 2]] "2x^2";
   assert_add [1, []; 3, [x, 1]; 2, [y, 1]] [2, []; 1, [x, 1]; 1, [z, 1]] "3 + 4x + 2y + z";
+  assert_add [1, []; 1, [x, 1; y, 2]] [1, [x, 2; y, 1]] "1 + xy^2 + x^2y";
   ()
 
 

source/analysis/type.ml

@@ -610,14 +610,18 @@ end = struct
     let total_degree_compare =
       Int.compare (sum_degrees left_variables) (sum_degrees right_variables)
     in
+    let compare_variable_and_degree
+        { Monomial.variable = left_variable; degree = left_degree }
+        { Monomial.variable = right_variable; degree = right_degree }
+      =
+      match compare_variable compare_t left_variable right_variable with
+      | result when not (Int.equal result 0) -> result
+      | _ -> Int.compare left_degree right_degree
+    in
     if total_degree_compare <> 0 then
       total_degree_compare
     else
-      let variable_list variables = List.map variables ~f:(fun { variable; _ } -> variable) in
-      List.compare
-        (compare_variable compare_t)
-        (variable_list left_variables)
-        (variable_list right_variables)
+      List.compare compare_variable_and_degree left_variables right_variables
 
 
   let normalize ~compare_t { constant_factor; variables } =