diff --git a/Rakefile b/Rakefile
index 774a3e7..8e6cff2 100644
--- a/Rakefile
+++ b/Rakefile
@@ -44,10 +44,12 @@ end
       .partition { |f| f.end_with? '.elna' }
 
     File.open t.name, 'w' do |output|
-      puts
-      puts(compiler * ' ')
+      compiler_command = compiler + sources
 
-      Open3.popen2(*compiler) do |cl_in, cl_out|
+      puts
+      puts(compiler_command * ' ')
+
+      Open3.popen2(*compiler_command) do |cl_in, cl_out|
         cl_in.write File.read(*sources)
         cl_in.close
 
@@ -104,7 +106,7 @@ task :backport do
     source
       .gsub(/^(var|type|const|begin)/) { |match| match.upcase }
       .gsub(/^[[:alnum:]]* ?module/) { |match| match.upcase }
-      .gsub(/\b(record|nil|or)\b/) { |match| match.upcase }
+      .gsub(/\b(record|nil|or|false|true)\b/) { |match| match.upcase }
       .gsub(/proc\(/, 'PROCEDURE(')
       .gsub(/ & /, ' AND ')
       .gsub(/ -> /, ': ')
diff --git a/source/CommandLineInterface.def b/source/CommandLineInterface.def
new file mode 100644
index 0000000..85be324
--- /dev/null
+++ b/source/CommandLineInterface.def
@@ -0,0 +1,15 @@
+DEFINITION MODULE CommandLineInterface;
+
+FROM Common IMPORT ShortString;
+
+TYPE
+  CommandLine = RECORD
+    input: ShortString;
+    lex: BOOLEAN;
+    parse: BOOLEAN
+  END;
+  PCommandLine = POINTER TO CommandLine;
+
+PROCEDURE parse_command_line(): PCommandLine;
+
+END CommandLineInterface.
diff --git a/source/CommandLineInterface.elna b/source/CommandLineInterface.elna
new file mode 100644
index 0000000..eb16b4f
--- /dev/null
+++ b/source/CommandLineInterface.elna
@@ -0,0 +1,75 @@
+implementation module CommandLineInterface;
+
+from SYSTEM import ADR, TSIZE;
+
+from Args import GetArg, Narg;
+from FIO import WriteString, WriteChar, WriteLine, StdErr;
+from Storage import ALLOCATE;
+from Strings import CompareStr, Length;
+from MemUtils import MemZero;
+
+from Common import ShortString;
+
+proc parse_command_line() -> PCommandLine;
+var
+  parameter: ShortString;
+  i: CARDINAL;
+  result: PCommandLine;
+  parsed: BOOLEAN;
+begin
+  i := 1;
+  ALLOCATE(result, TSIZE(CommandLine));
+  result^.lex := false;
+  result^.parse := false;
+  MemZero(ADR(result^.input), 256);
+
+  while (i < Narg()) & (result <> nil) do
+    parsed := GetArg(parameter, i);
+    parsed := false;
+
+    if CompareStr(parameter, '--lex') = 0 then
+      parsed := true;
+      result^.lex := true
+    end;
+    if CompareStr(parameter, '--parse') = 0 then
+      parsed := true;
+      result^.parse := true
+    end;
+    if parameter[0] <> '-' then
+      parsed := true;
+
+      if Length(result^.input) > 0 then
+        WriteString(StdErr, 'Fatal error: only one source file can be compiled at once. First given "');
+        WriteString(StdErr, result^.input);
+        WriteString(StdErr, '", then "');
+        WriteString(StdErr, parameter);
+        WriteString(StdErr, '".');
+        WriteLine(StdErr);
+        result := nil
+      end;
+      if result <> nil then
+        result^.input := parameter
+      end
+    end;
+    if parsed = false then
+      WriteString(StdErr, 'Fatal error: unknown command line options: ');
+
+      WriteString(StdErr, parameter);
+      WriteChar(StdErr, '.');
+      WriteLine(StdErr);
+
+      result := nil
+    end;
+
+    i := i + 1
+  end;
+  if (result <> nil) & (Length(result^.input) = 0) then
+    WriteString(StdErr, 'Fatal error: no input files.');
+    WriteLine(StdErr);
+    result := nil
+  end;
+
+  return result
+end;
+
+end CommandLineInterface.
diff --git a/source/Common.def b/source/Common.def
new file mode 100644
index 0000000..5925cbf
--- /dev/null
+++ b/source/Common.def
@@ -0,0 +1,6 @@
+DEFINITION MODULE Common;
+
+TYPE
+  ShortString = ARRAY[0..255] OF CHAR;
+
+END Common.
diff --git a/source/Common.elna b/source/Common.elna
new file mode 100644
index 0000000..7b8d623
--- /dev/null
+++ b/source/Common.elna
@@ -0,0 +1,3 @@
+implementation module Common;
+
+end Common.
diff --git a/source/Compiler.elna b/source/Compiler.elna
index 4e6ea19..207e348 100644
--- a/source/Compiler.elna
+++ b/source/Compiler.elna
@@ -5,11 +5,15 @@ from SYSTEM import ADR;
 
 from Lexer import Lexer, lexer_destroy, lexer_initialize;
 from Transpiler import transpile;
+from CommandLineInterface import PCommandLine, parse_command_line;
 
 var
   lexer: Lexer;
+  command_line: PCommandLine;
 
 begin
+  command_line := parse_command_line();
+
   lexer_initialize(ADR(lexer), StdIn);
 
   transpile(ADR(lexer));
diff --git a/source/Lexer.elna b/source/Lexer.elna
index 902e93a..19cfd34 100644
--- a/source/Lexer.elna
+++ b/source/Lexer.elna
@@ -217,7 +217,7 @@ var
   index: CARDINAL;
 begin
   index := 0;
-  result := TRUE;
+  result := true;
 
   while (index < Length(Keyword)) & (TokenStart <> TokenEnd) & result DO
     result := (Keyword[index] = TokenStart^) or (Lower(Keyword[index]) = TokenStart^);
@@ -409,11 +409,11 @@ begin
   end;
   if compare_keyword('TRUE', lexer^.Start, lexer^.Current) then
     token^.kind := lexerKindBoolean;
-    token^.booleanKind := TRUE
+    token^.booleanKind := true
   end;
   if compare_keyword('FALSE', lexer^.Start, lexer^.Current) then
     token^.kind := lexerKindBoolean;
-    token^.booleanKind := FALSE
+    token^.booleanKind := false
   end
 end;
 
diff --git a/source/Parser.def b/source/Parser.def
new file mode 100644
index 0000000..5b016de
--- /dev/null
+++ b/source/Parser.def
@@ -0,0 +1,3 @@
+DEFINITION MODULE Parser;
+
+END Parser.
diff --git a/source/Parser.elna b/source/Parser.elna
new file mode 100644
index 0000000..edd30e5
--- /dev/null
+++ b/source/Parser.elna
@@ -0,0 +1,3 @@
+module Parser;
+
+end Parser.
diff --git a/source/Transpiler.elna b/source/Transpiler.elna
index 9820193..ec96152 100644
--- a/source/Transpiler.elna
+++ b/source/Transpiler.elna
@@ -441,6 +441,14 @@ begin
       WriteString('NIL ');
       written_bytes := 1
     end;
+    if (token.kind = lexerKindBoolean) & token.booleanKind then
+      WriteString('TRUE ');
+      written_bytes := 1
+    end;
+    if (token.kind = lexerKindBoolean) & (~token.booleanKind) then
+      WriteString('FALSE ');
+      written_bytes := 1
+    end;
     if token.kind = lexerKindOr then
       WriteString('OR ');
       written_bytes := 1