json: add "null"

Author: Lenny222

src/libstd/json.rs

@@ -34,6 +34,8 @@ tag json {
     list(@[json]);
     /* Variant: dict */
     dict(map::hashmap<str,json>);
+    /* Variant: null */
+    null;
 }
 
 /*
@@ -233,6 +235,14 @@ fn from_str_bool(s: str) -> (option::t<json>, str) {
     }
 }
 
+fn from_str_null(s: str) -> (option::t<json>, str) {
+    if (str::starts_with(s, "null")) {
+        (some(null), str::slice(s, 4u, str::byte_len(s)))
+    } else {
+        (none, s)
+    }
+}
+
 fn from_str_helper(s: str) -> (option::t<json>, str) {
     let s = str::trim_left(s);
     if str::is_empty(s) { ret (none, s); }
@@ -243,6 +253,7 @@ fn from_str_helper(s: str) -> (option::t<json>, str) {
         '{' { from_str_dict(s) }
         '0' to '9' | '-' | '+' | '.' { from_str_float(s) }
         't' | 'f' { from_str_bool(s) }
+        'n' { from_str_null(s) }
         _ { ret (none, s); }
     }
 }

src/test/stdtest/json.rs

@@ -5,6 +5,11 @@ import option;
 import std::json::*;
 import option::{none, some};
 
+#[test]
+fn test_from_str_null() {
+    assert(from_str("null") == some(null));
+}
+
 #[test]
 fn test_from_str_num() {
     assert(from_str("3") == some(num(3f)));
@@ -31,6 +36,7 @@ fn test_from_str_bool() {
 fn test_from_str_list() {
     assert(from_str("[]") == some(list(@[])));
     assert(from_str("[true]") == some(list(@[boolean(true)])));
+    assert(from_str("[null]") == some(list(@[null])));
     assert(from_str("[3, 1]") == some(list(@[num(3f), num(1f)])));
     assert(from_str("[2, [4, 1]]") ==
         some(list(@[num(2f), list(@[num(4f), num(1f)])])));
@@ -44,6 +50,7 @@ fn test_from_str_list() {
 fn test_from_str_dict() {
     assert(from_str("{}") != none);
     assert(from_str("{\"a\": 3}") != none);
+    assert(from_str("{\"a\": null}") != none);
     assert(from_str("{\"a\": }") == none);
     assert(from_str("{\"a\" }") == none);
     assert(from_str("{\"a\"") == none);