From 70c4e33cf2cbb78a3e1dcfe72ca1ed00b983b797 Mon Sep 17 00:00:00 2001
From: Leonardo de Moura <leonardo@microsoft.com>
Date: Thu, 15 Nov 2018 13:05:29 -0800
Subject: [PATCH] feat(runtime/object): missing `string.iterator` builtin
 functions

---
 src/runtime/object.cpp | 38 ++++++++++++++++++++++++++++++++++++++
 src/runtime/object.h   |  3 +++
 2 files changed, 41 insertions(+)

diff --git a/src/runtime/object.cpp b/src/runtime/object.cpp
index 787d153061..44d815b39e 100644
--- a/src/runtime/object.cpp
+++ b/src/runtime/object.cpp
@@ -1198,6 +1198,21 @@ static std::string list_as_string(b_obj_arg lst) {
     return s;
 }
 
+static std::string rev_list_as_string(b_obj_arg lst) {
+    buffer<unsigned> codes;
+    b_obj_arg o = lst;
+    while (!is_scalar(o)) {
+        codes.push_back(unbox(cnstr_get(o, 0)));
+        o  = cnstr_get(o, 1);
+    }
+    std::reverse(codes.begin(), codes.end());
+    std::string s;
+    for (unsigned c : codes) {
+        push_unicode_scalar(s, c);
+    }
+    return s;
+}
+
 static obj_res string_to_list_core(std::string const & s, bool reverse = false) {
     buffer<unsigned> tmp;
     utf8_decode(s, tmp);
@@ -1477,6 +1492,29 @@ obj_res string_iterator_extract(b_obj_arg it1, b_obj_arg it2) {
     return mk_option_some(r);
 }
 
+obj_res string_iterator_mk(b_obj_arg l1, b_obj_arg l2) {
+    std::string s1 = rev_list_as_string(l1);
+    std::string s2 = list_as_string(l2);
+    size_t i       = s1.size();
+    std::reverse(s1.begin(), s1.end());
+    s1 += s2;
+    return mk_iterator(mk_string(s1), i, utf8_strlen(s2));
+}
+
+obj_res string_iterator_fst(b_obj_arg it) {
+    object * s = string_iterator_prev_to_string(it);
+    object * r = string_to_list_core(std::string(string_cstr(s), string_size(s)), true /* reverse */);
+    dec_ref(s);
+    return r;
+}
+
+obj_res string_iterator_snd(b_obj_arg it) {
+    object * s = string_iterator_remaining_to_string(it);
+    object * r = string_to_list_core(std::string(string_cstr(s), string_size(s)));
+    dec_ref(s);
+    return r;
+}
+
 // =======================================
 // Debugging helper functions
 
diff --git a/src/runtime/object.h b/src/runtime/object.h
index 312318e66f..d677c06390 100644
--- a/src/runtime/object.h
+++ b/src/runtime/object.h
@@ -1048,6 +1048,9 @@ obj_res string_iterator_prev_to_string(b_obj_arg it);
 obj_res string_iterator_to_string(b_obj_arg it);
 obj_res string_iterator_to_end(obj_arg it);
 obj_res string_iterator_extract(b_obj_arg it1, b_obj_arg it2);
+obj_res string_iterator_mk(obj_arg cs1, obj_arg cs2);
+obj_res string_iterator_fst(b_obj_arg it);
+obj_res string_iterator_snd(b_obj_arg it);
 
 bool string_eq(b_obj_arg s1, b_obj_arg s2);
 inline bool string_ne(b_obj_arg s1, b_obj_arg s2) { return !string_eq(s1, s2); }