Add math assignment operators

grammar.coffee

@@ -182,9 +182,6 @@ module.exports =
 
       var_assignment: -> seq(@type_expression, "=", @expression)
 
-      type_modifier: -> choice(
-        keyword("const"))
-
       expression: -> choice(
         @bool_op,
         @math_op,
@@ -248,7 +245,12 @@ module.exports =
           @field_access,
           @deref_field_access,
           @subscript_access),
-        "=",
+        choice(
+          "=",
+          "+=",
+          "-=",
+          "*=",
+          "/="),
         @expression))
 
       compound_literal: -> seq(

grammar_test/expressions.txt

@@ -105,6 +105,10 @@ int main() {
   d.e = 3;
   f->g = 4;
   h[i] = j;
+  k += l;
+  m -= o;
+  n *= p;
+  q /= r;
 }
 
 ---
@@ -115,7 +119,11 @@ int main() {
     (expression_statement (assignment (identifier) (assignment (deref (identifier)) (number))))
     (expression_statement (assignment (field_access (identifier) (identifier)) (number)))
     (expression_statement (assignment (deref_field_access (identifier) (identifier)) (number)))
-    (expression_statement (assignment (subscript_access (identifier) (identifier)) (identifier)))))
+    (expression_statement (assignment (subscript_access (identifier) (identifier)) (identifier)))
+    (expression_statement (assignment (identifier) (identifier)))
+    (expression_statement (assignment (identifier) (identifier)))
+    (expression_statement (assignment (identifier) (identifier)))
+    (expression_statement (assignment (identifier) (identifier)))))
 
 ============================================
 Pointer operations