diff --git a/source/CommandLine.def b/source/CommandLine.def
new file mode 100644
index 0000000..37fd7fa
--- /dev/null
+++ b/source/CommandLine.def
@@ -0,0 +1,3 @@
+DEFINITION MODULE CommandLine;
+
+END CommandLine.
diff --git a/source/CommandLine.mod b/source/CommandLine.mod
new file mode 100644
index 0000000..215f7c3
--- /dev/null
+++ b/source/CommandLine.mod
@@ -0,0 +1,3 @@
+MODULE CommandLine;
+
+END CommandLine.
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.mod b/source/CommandLineInterface.mod
new file mode 100644
index 0000000..2b33668
--- /dev/null
+++ b/source/CommandLineInterface.mod
@@ -0,0 +1,74 @@
+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;
+
+PROCEDURE 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()) AND (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) AND (Length(result^.input) = 0) THEN
+    WriteString(StdErr, 'Fatal error: no input files.');
+    WriteLine(StdErr);
+    result := NIL
+  END;
+
+  RETURN result
+END parse_command_line;
+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.mod b/source/Common.mod
new file mode 100644
index 0000000..135d3a9
--- /dev/null
+++ b/source/Common.mod
@@ -0,0 +1,3 @@
+IMPLEMENTATION MODULE Common;
+
+END Common.
diff --git a/source/Compiler.mod b/source/Compiler.mod
index c6b3e09..9e2ed04 100644
--- a/source/Compiler.mod
+++ b/source/Compiler.mod
@@ -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/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.mod b/source/Parser.mod
new file mode 100644
index 0000000..bf39cc7
--- /dev/null
+++ b/source/Parser.mod
@@ -0,0 +1,3 @@
+MODULE Parser;
+
+END Parser.
diff --git a/source/Transpiler.mod b/source/Transpiler.mod
index 63ce824..e5c0317 100644
--- a/source/Transpiler.mod
+++ b/source/Transpiler.mod
@@ -421,6 +421,14 @@ BEGIN
       WriteString('NIL ');
       written_bytes := 1
     END;
+    IF (token.kind = lexerKindBoolean) AND token.booleanKind THEN
+      WriteString('TRUE ');
+      written_bytes := 1
+    END;
+    IF (token.kind = lexerKindBoolean) AND (~token.booleanKind) THEN
+      WriteString('FALSE ');
+      written_bytes := 1
+    END;
     IF token.kind = lexerKindOr THEN
       WriteString('OR ');
       written_bytes := 1