feat: allow guards in deflua functions

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+- `deflua` function can now specify guards when using or not using state
+
 ## [v0.2.1] - 2025-05-14
 
 ### Added

lib/lua/api.ex

@@ -122,7 +122,7 @@ defmodule Lua.API do
   @doc """
   Defines a function that can be exposed in Lua through `Lua.load_api/3`
 
-      deflua add_two(number) do
+      deflua add_two(number) when is_number(number) do
         number + 2
       end
 
@@ -143,6 +143,18 @@ defmodule Lua.API do
         {[], Lua.set!(lua, [key])}
       end
 
+  ## Using guards
+
+  Since `deflua` uses non-conventional syntax to receive the current state, make sure
+  you specifiy the `when` clause and guards first, e.g.
+
+      deflua set_int(key, value) when is_integer(value), state do
+        # Return nothing but modify the state
+        {[], Lua.set!(lua, [key])}
+      end
+
+  Specifyiing the `when` cluase and guards last will result in a confusing error message.
+
   ## Variadic functions
 
   Technically, all Lua functions are variadic, which means they can receive
@@ -164,13 +176,20 @@ defmodule Lua.API do
 
   """
   defmacro deflua(fa, state, rest) do
+    name =
+      case fa do
+        {:when, _, [{name, _, _} | _]} -> name
+        {name, _, _} -> name
+      end
+
     {fa, _acc} =
-      Macro.prewalk(fa, false, fn
-        {name, context, args}, false -> {{name, context, args ++ List.wrap(state)}, true}
-        ast, true -> {ast, true}
-      end)
+      Macro.prewalk(fa, :ok, fn
+        {^name, context, args}, acc ->
+          {{name, context, args ++ List.wrap(state)}, acc}
 
-    {name, _, _} = fa
+        ast, acc ->
+          {ast, acc}
+      end)
 
     quote do
       @lua_function validate_func!(

test/lua/api_test.exs

@@ -299,5 +299,41 @@ defmodule Lua.APITest do
       assert module.fail(1, 2) == 3
       assert module.fail(1, "2") == "rescued"
     end
+
+    test "deflua functions can have guards" do
+      assert [{module, _}] =
+               Code.compile_string("""
+               defmodule WithGuards do
+                 use Lua.API
+
+                 deflua has_a_guard(a) when is_integer(a) do
+                   a
+                 end
+
+                 deflua has_a_guard(a) when is_binary(a) and not is_boolean(a) do
+                   a
+                 end
+
+                 deflua has_a_guard(_) do
+                   "not a int"
+                 end
+
+                 deflua with_state(a) when is_integer(a), state do
+                   {a, state}
+                 end
+
+                 deflua with_state(_), state do
+                   {"not a int", state}
+                 end
+               end
+               """)
+
+      assert module.has_a_guard(1) == 1
+      assert module.has_a_guard("foo") == "foo"
+      assert module.has_a_guard(true) == "not a int"
+
+      assert {1, _} = module.with_state(1, Lua.new())
+      assert {"not a int", _} = module.with_state(true, Lua.new())
+    end
   end
 end