add if, ifelse, return

lib.nix

@@ -18,6 +18,9 @@ let
   inherit (builtins) isString isFloat isInt isBool isList isAttrs isNull isPath;
   inherit (builtins) concatStringsSep filter mapAttrs attrValues;
 
+  isNotNull = v: !(isNull v);
+  excludeNull = expr: filter isNotNull expr;
+
   ################################################################################
   # Utils
   ################################################################################
@@ -83,16 +86,12 @@ let
   kw_in = raw "in";
   kw_then = raw "then";
   kw_else = raw "else";
-  kw_elseif = raw "elseif";
   kw_local = raw "local";
   kw_for = raw "for";
   kw_do = raw "do";
   kw_until = raw "until";
   kw_while = raw "while";
   kw_repeat = raw "repeat";
-  # kw_false = raw "false";
-  # kw_true = raw "true";
-  # kw_nil = raw "nil";
 
   op = operation: left: right: wrapParen (join " ${operation} " [ left right ]);
 
@@ -128,6 +127,18 @@ let
       ++ [ kw_end ])
     );
 
+  return = expr: spaceBetween ([ kw_return expr ]);
+  return_void = return null;
+
+  ifelse = condition: trueBody: falseBody:
+    (concatLines
+      ([ (spaceBetween [ kw_if condition kw_then ]) ]
+        ++ trueBody
+        ++ (if falseBody != [ ] then [ kw_else ] ++ falseBody else [ ])
+        ++ [ kw_end ])
+    );
+  if' = condition: trueBody: ifelse condition trueBody [ ];
+
   isLuaNil = expr: getType expr == "nil";
   LuaNil = { _type = "nil"; };
 
@@ -144,7 +155,6 @@ let
   toLuaList = onValue: expr:
     let
       wrapObj = expr: "{ ${concatStringsSep ", " expr} }";
-      excludeNull = expr: filter (v: !(isNull v)) expr;
     in
     wrapObj (excludeNull (map onValue expr));
   toLuaNamedField = name: expr:
@@ -154,7 +164,7 @@ let
 
   toLuaInternal = depth: expr:
     let nextDepth = depth + 1; in
-    if isJoin expr then concatStringsSep expr.sep (map (toLuaInternal depth) expr.parts)
+    if isJoin expr then concatStringsSep expr.sep (map (toLuaInternal depth) (excludeNull expr.parts))
     else if isLuaNil expr then "nil"
     else if isRaw expr then expr.raw
     else if isNamedField expr then
@@ -181,13 +191,15 @@ in
 
   inherit LuaNil;
   inherit raw join concat concatLines pipe;
-  inherit namedField call require local set func;
+  inherit namedField call require local set func ifelse if';
 
   inherit op;
   inherit eq ne gt lt gte lte;
   inherit add sub mul div mod exp;
   inherit and or not;
 
+  inherit return return_void;
+
   # useful alias
   var = raw;
 }

lib.test.nix

@@ -178,4 +178,62 @@ with nix2lua; pkgs.lib.runTests {
       end
     '';
   };
+  "test returns if statement" = {
+    expr = toLua (if' (eq 10 10) [
+      (call "print" [ 10 ])
+    ]);
+    expected = ''
+      if (10 == 10) then
+      print(10)
+      end
+    '';
+  };
+  "test returns if else statement" = {
+    expr = toLua (ifelse (eq 10 10) [
+      (call "print" [ "10 == 10" ])
+    ] [
+      (call "print" [ "10 != 10" ])
+    ]);
+    expected = ''
+      if (10 == 10) then
+      print("10 == 10")
+      else
+      print("10 != 10")
+      end
+    '';
+  };
+  "test returns a deep if else statement" = {
+    expr = toLua (ifelse (eq 10 10) [
+      (if' true [ (call "print" [ "yes" ]) ])
+    ] [
+      (if' true [ (call "print" [ "no" ]) ])
+    ]);
+    expected = ''
+      if (10 == 10) then
+      if true then
+      print("yes")
+      end
+
+      else
+      if true then
+      print("no")
+      end
+
+      end
+    '';
+  };
+  "test returns a returns keyword" = {
+    expr = toLua (ifelse (eq 10 10) [
+      return_void
+    ] [
+      (return 10)
+    ]);
+    expected = ''
+      if (10 == 10) then
+      return
+      else
+      return 10
+      end
+    '';
+  };
 }