add placeholder support for backcall operator.

3 files changed, 38 insertions, 4 deletions

diff --git a/spec/inputs/backcall.moon b/spec/inputs/backcall.moon
index a65bb0a..f5d0046 100644
--- a/spec/inputs/backcall.moon
+++ b/spec/inputs/backcall.moon
@@ -30,8 +30,14 @@ f = ->
 998 |> func2 "abc", 233 |> func0 |> func1
 998 |> func0("abc", 233) |> func1 |> func2
 
+1 |> f 2, 3, 4, 5
+val(2) |> f 1, _, 3, 4, 5
+arr[3] |> f 1, 2, _, 4, 5
+
+a = {"1","2","3"} |> table.concat("") |> tonumber |> f1(1, 2, 3, _) |> f2(1, _, 3)
+
 do
-        (x)<-map {1,2,3}
+        (x)<- map {1,2,3}
         x * 2
 
 do
diff --git a/src/MoonP/ast.hpp b/src/MoonP/ast.hpp
index 8bcfc21..b56cfde 100644
--- a/src/MoonP/ast.hpp
+++ b/src/MoonP/ast.hpp
@@ -399,6 +399,18 @@ public:
                 node->release();
         }
 
+        bool swap(ast_node* node, ast_node* other) {
+                for (auto it = m_objects.begin(); it != m_objects.end(); ++it) {
+                        if (*it == node) {
+                                *it = other;
+                                other->retain();
+                                node->release();
+                                return true;
+                        }
+                }
+                return false;
+        }
+
          const node_container& objects() const {
                 return m_objects;
         }
diff --git a/src/MoonP/moon_compiler.cpp b/src/MoonP/moon_compiler.cpp
index 30adbae..d009fc9 100644
--- a/src/MoonP/moon_compiler.cpp
+++ b/src/MoonP/moon_compiler.cpp
@@ -29,7 +29,7 @@ inline std::string s(std::string_view sv) {
 }
 
 const char* moonScriptVersion() {
-        return "0.5.0-r0.1.0";
+        return "0.5.0-r0.1.1";
 }
 
 class MoonCompiler {
@@ -1528,10 +1528,26 @@ private:
                                                 }
                                                 if (isChainValueCall(chainValue)) {
                                                         auto last = chainValue->items.back();
+                                                        _ast_list* args = nullptr;
                                                         if (auto invoke = ast_cast<InvokeArgs_t>(last)) {
-                                                                invoke->args.push_front(arg);
+                                                                args = &invoke->args;
                                                         } else {
-                                                                ast_to<Invoke_t>(last)->args.push_front(arg);
+                                                                args = &(ast_to<Invoke_t>(last)->args);
+                                                        }
+                                                        bool findPlaceHolder = false;
+                                                        for (auto a : args->objects()) {
+                                                                auto name = singleVariableFrom(a);
+                                                                if (name == "_"sv) {
+                                                                        if (!findPlaceHolder) {
+                                                                                args->swap(a, arg);
+                                                                                findPlaceHolder = true;
+                                                                        } else {
+                                                                                throw std::logic_error(_info.errorMessage("backcall placeholder can be used only in one place."sv, a));
+                                                                        }
+                                                                }
+                                                        }
+                                                        if (!findPlaceHolder) {
+                                                                args->push_front(arg);
                                                         }
                                                 } else {
                                                         auto invoke = x->new_ptr<Invoke_t>();