add placeholder support for backcall operator.

1 files changed, 19 insertions, 3 deletions

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>();