Fix the //= operator.

Closes #62.

parser.y

@@ -164,6 +164,16 @@ static block gen_format(block a, jv fmt) {
   return BLOCK(a, gen_call("format", BLOCK(gen_lambda(gen_const(fmt)))));
 }
 
+static block gen_definedor_assign(block object, block val) {
+  block tmp = block_bind(gen_op_var_unbound(STOREV, "tmp"),
+                         gen_noop(), OP_HAS_VARIABLE);
+  return BLOCK(gen_op_simple(DUP),
+               val, tmp,
+               gen_call("_modify", BLOCK(gen_lambda(object),
+                                         gen_lambda(gen_definedor(gen_noop(), 
+                                                                  gen_op_var_bound(LOADV, tmp))))));
+}
+ 
 static block gen_update(block object, block val, int optype) {
   block tmp = block_bind(gen_op_var_unbound(STOREV, "tmp"),
                          gen_noop(), OP_HAS_VARIABLE);
@@ -235,7 +245,7 @@ Exp "//" Exp {
 } |
 
 Exp "//=" Exp {
-  $$ = gen_update($1, gen_definedor(gen_noop(), $3), 0);
+  $$ = gen_definedor_assign($1, $3);
 } |
 
 Exp "|=" Exp {

tests/all.test

@@ -475,10 +475,9 @@ def inc(x): x |= .+1; inc(.[].a)
 [{"foo":[1,2], "bar": 42}, {"foo":[1], "bar": null}, {"foo":[null,false,3], "bar": 18}, {"foo":[], "bar":42}, {"foo": [null,false,null], "bar": 41}]
 [[1,2], [1], [3], [42], [41]]
 
-# FIXME: behaviour of update operators
-# .[] //= .[0]
-# ["hello",true,false,[false],null]
-# ["hello",true,"hello",[false],"hello"]
+.[] //= .[0]
+["hello",true,false,[false],null]
+["hello",true,"hello",[false],"hello"]
 
 .[] | [.[0] and .[1], .[0] or .[1]]
 [[true,[]], [false,1], [42,null], [null,false]]