diff --git a/lib.nix b/lib.nix
index fc0886d..72e0baf 100644
--- a/lib.nix
+++ b/lib.nix
@@ -26,6 +26,9 @@ let
   ################################################################################
 
   error = message: throw "[nix2lua] ${message}";
+  validationError = expr: message:
+    let val = if builtins.isFunction expr then "Function" else "Value '${toString expr}'"; in
+    error "${val} ${message}";
   warn = msg: builtins.trace "[nix2lua] warning: ${msg}";
   deprecated = before: now: warn "`${before}` is deprecated. Use `${now}` instead";
 
@@ -34,11 +37,11 @@ let
   validString = expr:
     if isRaw expr then validString expr.raw
     else if isString expr || isPath expr then toString expr
-    else error "Value '${toString expr}' is not a valid string";
+    else validationError expr "is not a valid string";
 
   validFuncName = fnName:
     if isString fnName && builtins.stringLength fnName > 0 then raw fnName
-    else error "Value '${toString fnName}' is not a valid function name";
+    else validationError fnName "is not a valid function name";
 
   ################################################################################
   # Low-Level
@@ -46,25 +49,16 @@ let
 
   isRaw = expr: getType expr == "raw";
   raw = expr:
-    if isRaw expr then
-      { _type = "raw"; raw = expr.raw; }
-    else if isString expr then
-      { _type = "raw"; raw = expr; }
-    else
-      error "Value '${toString expr}' is not supported for a raw type";
+    if isRaw expr then { _type = "raw"; raw = expr.raw; }
+    else if isString expr then { _type = "raw"; raw = expr; }
+    else validationError expr "is not supported for a raw type";
 
   isJoin = expr: getType expr == "_join";
   join = sep: expr:
     if isList expr then { _type = "_join"; sep = validString sep; parts = expr; }
-    else error "Value '${toString expr}' is not supported for a join type";
+    else validationError expr "is not supported for a join type";
 
   concat = join "";
-  concatLines = lines:
-    join "\n" (
-      lines
-      # add an empty line at the end
-      ++ [ (raw "") ]
-    );
   pipe = join ".";
   pipe1 = lft: rgt: pipe [ lft rgt ];
   spaceBetween = join " ";
@@ -74,10 +68,17 @@ let
   wrapParen = wrap "(" ")";
 
   call = fnName: args:
-    concat [ (validFuncName fnName) (wrapParen (join ", " args)) ];
+    concat [
+      (validFuncName fnName)
+      (wrapParen (
+        if isList args then join ", " args
+        else if builtins.isFunction args then validationError args "is not supported to call args"
+        else args
+      ))
+    ];
   call0 = fnName: call fnName [ ];
   call1 = fnName: arg: call fnName [ arg ];
-  require = name: call1 "require" name;
+  require = name: call "require" name;
 
   kw_and = raw "and";
   kw_or = raw "or";
@@ -117,36 +118,38 @@ let
   or = op kw_or;
   not = expr: spaceBetween [ kw_not expr ];
 
+  # Type: validBlockBody :: a -> [b]
+  validBlockBody = body:
+    if isList body then body
+    else if isAttrs body then [ body ]
+    else validationError body "is not valid block body";
+
   local = expr: spaceBetween [ kw_local expr ];
   set = variable: value: join " = " [ (raw variable) value ];
   func = fnName: params: body:
-    let
-      f =
-        if isList body then concatLines
-        else if isAttrs body then spaceBetween
-        else error "Value ${toString body} is not a valid function body";
-    in
-    (f
+    (spaceBetween
       ([
         (concat [
           (spaceBetween [ kw_function (validFuncName fnName) ])
           (wrapParen (join ", " (map raw params)))
         ])
       ]
-      ++ (if isList body then body else if isAttrs body then [ body ] else [ ])
+      ++ (validBlockBody body)
       ++ [ kw_end ])
     );
+  func0 = fnName: func fnName [ ];
   lambda = func "";
   lambda0 = lambda [ ];
 
   return = expr: spaceBetween ([ kw_return expr ]);
-  return_void = return null;
+  return_void = return
+    null;
 
   ifelse = condition: trueBody: falseBody:
-    (concatLines
-      ([ (spaceBetween [ kw_if condition kw_then ]) ]
-        ++ trueBody
-        ++ (if falseBody != [ ] then [ kw_else ] ++ falseBody else [ ])
+    (spaceBetween
+      ([ kw_if condition kw_then ]
+        ++ (validBlockBody trueBody)
+        ++ (if falseBody != [ ] then [ kw_else ] ++ (validBlockBody falseBody) else [ ])
         ++ [ kw_end ])
     );
   if' = condition: trueBody: ifelse condition trueBody [ ];
@@ -198,17 +201,18 @@ in
   mkLuaRaw = deprecated "mkLuaRaw" "raw" raw;
   mkCall = deprecated "mkCall" "call" call;
   mkNamedField = deprecated "mkNamedField" "namedField" namedField;
+  concatLines = deprecated "concatLines" "spaceBetween" spaceBetween;
 
   inherit toLua;
 
   inherit LuaNil;
-  inherit raw join concat concatLines;
+  inherit raw join concat spaceBetween;
   inherit pipe pipe1;
 
   inherit namedField require local set ifelse if';
 
   inherit call call0 call1;
-  inherit func lambda lambda0;
+  inherit func func0 lambda lambda0;
 
   inherit op;
   inherit eq ne gt lt gte lte;
diff --git a/lib.test.nix b/lib.test.nix
index 57b95de..8731185 100644
--- a/lib.test.nix
+++ b/lib.test.nix
@@ -33,11 +33,11 @@ with nix2lua; pkgs.lib.runTests {
   };
   "test returns a lua string" = {
     expr = toLua "hello world";
-    expected = "\"hello world\"";
+    expected = ''"hello world"'';
   };
   "test returns a path as a lua string" = {
     expr = toLua /hello/world;
-    expected = "\"/hello/world\"";
+    expected = ''"/hello/world"'';
   };
   "test returns an integer number" = {
     expr = toLua 10;
@@ -61,11 +61,11 @@ with nix2lua; pkgs.lib.runTests {
   };
   "test returns table with all primitive types" = {
     expr = toLua [ "hello" 10 10.1 true ];
-    expected = "{ \"hello\", 10, 10.100000, true }";
+    expected = ''{ "hello", 10, 10.100000, true }'';
   };
   "test returns table without null values" = {
     expr = toLua [ null "hello" null 10 null 10.1 null true null ];
-    expected = "{ \"hello\", 10, 10.100000, true }";
+    expected = ''{ "hello", 10, 10.100000, true }'';
   };
   "test returns named table" = {
     expr = toLua {
@@ -75,11 +75,11 @@ with nix2lua; pkgs.lib.runTests {
       success = true;
       fail = false;
     };
-    expected = "{ [\"fail\"] = false, [\"float\"] = 10.100000, [\"foo\"] = \"hello\", [\"int\"] = 10, [\"success\"] = true }";
+    expected = ''{ ["fail"] = false, ["float"] = 10.100000, ["foo"] = "hello", ["int"] = 10, ["success"] = true }'';
   };
   "test returns named table without nullable items" = {
     expr = toLua { foo = "hello"; bar = null; };
-    expected = "{ [\"foo\"] = \"hello\" }";
+    expected = ''{ ["foo"] = "hello" }'';
   };
   "test returns recursive named table" = {
     expr = toLua {
@@ -89,11 +89,11 @@ with nix2lua; pkgs.lib.runTests {
         };
       };
     };
-    expected = "{ [\"first\"] = { [\"second\"] = { [\"last\"] = \"hello\" } } }";
+    expected = ''{ ["first"] = { ["second"] = { ["last"] = "hello" } } }'';
   };
   "test return recursive table" = {
     expr = toLua [ [ [ "foo" ] "bar" ] ];
-    expected = "{ { { \"foo\" }, \"bar\" } }";
+    expected = ''{ { { "foo" }, "bar" } }'';
   };
   "test returns table with one named field" = {
     expr = toLua [
@@ -101,7 +101,7 @@ with nix2lua; pkgs.lib.runTests {
       (namedField "foo" "hello")
       10
     ];
-    expected = "{ \"foo\", [\"foo\"] = \"hello\", 10 }";
+    expected = ''{ "foo", ["foo"] = "hello", 10 }'';
   };
   "test returns raw string" = {
     expr = toLua (raw "hello");
@@ -113,7 +113,7 @@ with nix2lua; pkgs.lib.runTests {
   };
   "test returns path as string" = {
     expr = toLua /foo/bar;
-    expected = "\"/foo/bar\"";
+    expected = ''"/foo/bar"'';
   };
   "test throws an error when you try to use named field withoun table" = {
     expr = tryEval (toLua (namedField "foo" "bar"));
@@ -121,17 +121,14 @@ with nix2lua; pkgs.lib.runTests {
   };
   "test returns call function with arguments" = {
     expr = toLua (call "root_pattern" [ "deno.json" "deno.jsonc" ]);
-    expected = "root_pattern(\"deno.json\", \"deno.jsonc\")";
+    expected = ''root_pattern("deno.json", "deno.jsonc")'';
   };
-  "test returns concated lines" = {
-    expr = toLua (concatLines [
+  "test returns concated expressions" = {
+    expr = toLua (spaceBetween [
       (call "foo" [ 1 2 ])
       (call "bar" [ "baz" "biz" ])
     ]);
-    expected = ''
-      foo(1, 2)
-      bar("baz", "biz")
-    '';
+    expected = ''foo(1, 2) bar("baz", "biz")'';
   };
   "test returns a pipe with many function call" = {
     expr = toLua (pipe [
@@ -149,18 +146,13 @@ with nix2lua; pkgs.lib.runTests {
     expected = "local parser_config.d2 = {  }";
   };
   "test returns all operations" = {
-    expr = toLua (concatLines [
-      (eq (mul (add 1 2) (sub 2 1)) 3)
-      (not (eq (mul (add 1 2) (sub 2 1)) 3))
-      (not 10)
-      (gt 10 5)
+    expr = toLua (spaceBetween [
+      (set "a" (eq (mul (add 1 2) (sub 2 1)) 3))
+      (set "b" (not (eq (mul (add 1 2) (sub 2 1)) 3)))
+      (set "c" (not 10))
+      (set "d" (gt 10 5))
     ]);
-    expected = ''
-      (((1 + 2) * (2 - 1)) == 3)
-      not (((1 + 2) * (2 - 1)) == 3)
-      not 10
-      (10 > 5)
-    '';
+    expected = ''a = (((1 + 2) * (2 - 1)) == 3) b = not (((1 + 2) * (2 - 1)) == 3) c = not 10 d = (10 > 5)'';
   };
   "test returns rendered condition" = {
     expr = toLua (set "name"
@@ -168,82 +160,42 @@ with nix2lua; pkgs.lib.runTests {
     );
     expected = "name = ((a >= 1) and (a <= 10))";
   };
-  "test returns defined multiline function" = {
+  "test returns defined function" = {
     expr = toLua (func "hello" [ "a" "b" ] [
-      (eq (mul (add (var "a") 2) (sub 2 1)) 3)
-      (not (eq (mul (add (var "b") 2) (sub 2 1)) 3))
-      (not 10)
-      (gt 10 5)
+      (set "a" (eq (mul (add 1 2) (sub 2 1)) 3))
+      (set "b" (not (eq (mul (add 1 2) (sub 2 1)) 3)))
+      (set "c" (not 10))
+      (set "d" (gt 10 5))
     ]);
-    expected = ''
-      function hello(a, b)
-      (((a + 2) * (2 - 1)) == 3)
-      not (((b + 2) * (2 - 1)) == 3)
-      not 10
-      (10 > 5)
-      end
-    '';
+    expected = ''function hello(a, b) a = (((1 + 2) * (2 - 1)) == 3) b = not (((1 + 2) * (2 - 1)) == 3) c = not 10 d = (10 > 5) end'';
   };
   "test returns defined singleline function" = {
     expr = toLua (func "hello" [ "a" ] (call1 "h.world" (var "a")));
     expected = "function hello(a) h.world(a) end";
   };
   "test returns if statement" = {
-    expr = toLua (if' (eq 10 10) [
-      (call "print" [ 10 ])
-    ]);
-    expected = ''
-      if (10 == 10) then
-      print(10)
-      end
-    '';
+    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")
+      (call "print" "10 == 10")
     ] [
-      (call "print" [ "10 != 10" ])
+      (call "print" "10 != 10")
+      (call "print" "10 != 10")
     ]);
-    expected = ''
-      if (10 == 10) then
-      print("10 == 10")
-      else
-      print("10 != 10")
-      end
-    '';
+    expected = ''if (10 == 10) then print("10 == 10") print("10 == 10") else print("10 != 10") 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
-    '';
+    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
-    '';
+    expr = toLua (ifelse (eq 10 10) return_void (return 10));
+    expected = ''if (10 == 10) then return else return 10 end'';
   };
 }