add do statement

README.md

@@ -104,14 +104,14 @@ Add `nix2lua` as input to your `flake.nix`
 
 `pipe expr`
 
-> Joins expressions with a '.' (dot) separator.
-> If list of expressions contains a string it will
-> convert to the raw.
+> Joins expressions with a '.' (dot) separator. If list of expressions contains
+> a string it will convert to the raw.
 >
 > ```nix
 > toLua (pipe ["vim" "opt" "line"]);
 > # vim.opt.line
 > ```
+>
 > ```nix
 > toLua (pipe ["luasnip" (call0 "setup")]);
 > # luasnip.setup()
@@ -128,8 +128,8 @@ Add `nix2lua` as input to your `flake.nix`
 
 `spaceBetween expr`
 
-> Join expressions with a space separator. You can use it to separate
-> all expressions in the Lua configuration.
+> Join expressions with a space separator. You can use it to separate all
+> expressions in the Lua configuration.
 >
 > This is alias for `join " "`
 >
@@ -145,13 +145,14 @@ Add `nix2lua` as input to your `flake.nix`
 
 > Util to call a Lua function with arguments.
 >
-> If `args` is list that each list item render as function argument.
-> Otherwise, it will be rendered as first argument.
+> If `args` is list that each list item render as function argument. Otherwise,
+> it will be rendered as first argument.
 >
 > ```nix
 > toLua (call "setup" [ "foo" "bar" ]);
 > # setup("foo", "bar")
 > ```
+>
 > ```nix
 > toLua (call "setup" { foo = "bar" });
 > # or: toLua (call "setup" [{ foo = "bar" }]);
@@ -171,9 +172,8 @@ Add `nix2lua` as input to your `flake.nix`
 
 `call1 fnName arg`
 
-> Call a Lua function with one argument.
-> This is useful when a Lua function has only one argument of type list,
-> and we want to avoid using an inner list.
+> Call a Lua function with one argument. This is useful when a Lua function has
+> only one argument of type list, and we want to avoid using an inner list.
 >
 > This is alias for `call fnName [arg]`.
 >
@@ -187,6 +187,7 @@ Add `nix2lua` as input to your `flake.nix`
 > Call a require function to import module with `name`.
 >
 > This is alias for `call "require" name`.
+>
 > ```nix
 > toLua (require "luasnip")
 > # require("luasnip")
@@ -233,6 +234,7 @@ Add `nix2lua` as input to your `flake.nix`
 > ```
 >
 > Useful aliases:
+>
 > ```
 > lset = l: r: local (set l r);
 > ```
@@ -247,6 +249,7 @@ Add `nix2lua` as input to your `flake.nix`
 > ```
 >
 > Useful aliases:
+>
 > ```
 > func0 = fnName: func fnName [ ];
 >
@@ -256,8 +259,8 @@ Add `nix2lua` as input to your `flake.nix`
 
 `lambda params body`
 
-> Define a lambda function with specific parameters and body.
-> Useful to use Lua function inline.
+> Define a lambda function with specific parameters and body. Useful to use Lua
+> function inline.
 >
 > ```nix
 > toLua (call "setup" {
@@ -267,6 +270,7 @@ Add `nix2lua` as input to your `flake.nix`
 > ```
 >
 > Useful aliases:
+>
 > ```
 > lambda0 = lambda [ ];
 > ```
@@ -295,6 +299,7 @@ Add `nix2lua` as input to your `flake.nix`
 > ```
 >
 > Useful aliases:
+>
 > ```
 > return_void = return null;
 > ```
@@ -317,6 +322,21 @@ Add `nix2lua` as input to your `flake.nix`
 > # if (10 == 10) print("yes") end
 > ```
 
+`do body`
+
+> Limit scope of the variables
+>
+> ```nix
+> toLua (do [(requireTo "foo" "foo")])
+> # do local set foo = require("foo") end
+> ```
+>
+> Aliases:
+>
+> ```
+> scope = do
+> ```
+
 # License
 
 GNU General Public License v3.0 or later

lib.nix

@@ -127,7 +127,9 @@ let
     if isJoin expr && expr.sep == "." then expr
     else if isRaw expr then expr
     else raw (validString expr);
-  set = var: val: join " = " [ (validSetVariable var) val ];
+  set = var: val:
+    if val == null then null
+    else join " = " [ (validSetVariable var) val ];
 
   # Type: validBlockBody :: a -> [b]
   validBlockBody = body:
@@ -170,6 +172,8 @@ let
     ]));
   if' = condition: trueBody: ifelse condition trueBody [ ];
 
+  do = body: spaceBetween [ kw_do ] ++ body ++ [ kw_end ];
+
   isLuaNil = expr: getType expr == "nil";
   LuaNil = { _type = "nil"; };
 
@@ -228,10 +232,19 @@ in
   inherit toLua;
 
   inherit LuaNil;
-  inherit raw join concat spaceBetween;
+
+  inherit raw;
+  var = raw;
+  vars = map raw;
+
+  inherit join concat spaceBetween;
   inherit pipe pipe1;
 
-  inherit namedField local;
+  inherit local;
+
+  inherit namedField;
+  nf = namedField;
+
   inherit ifelse if';
   inherit set;
   lset = l: r: local (set l r);
@@ -249,8 +262,6 @@ in
 
   inherit return return_void;
 
-  # useful aliases
-  var = raw;
-  vars = map raw;
-  nf = namedField;
+  inherit do;
+  scope = do;
 }

lib.test.nix

@@ -193,6 +193,10 @@ with nix2lua; pkgs.lib.runTests {
     expr = toLua (lset "parser_config.d2" { });
     expected = "local parser_config.d2 = {  }";
   };
+  "test skips a var definition if value is null" = {
+    expr = toLua (set "vim.opt.number" null);
+    expected = null;
+  };
   "test returns all operations" = {
     expr = toLua (spaceBetween [
       (set "a" (eq (mul (add 1 2) (sub 2 1)) 3))