diff --git a/src/yacc/parser.y b/src/yacc/parser.y
index 48db348..ddcae10 100644
--- a/src/yacc/parser.y
+++ b/src/yacc/parser.y
@@ -63,7 +63,8 @@
 %left OpBitand OpBitor OpBitxor OpBitnot
 
 %%
-program: statementlist;
+program: statementlist
+        | fundef;
 
 expr: ValFloat
     | ValInt
@@ -75,10 +76,33 @@ expr: ValFloat
 exprlist: expr ',' exprlist
         | expr;
 
-paramlist: '(' exprlist ')' paramlist
-    | '(' exprlist ')';
+argumentlist: argumentlist '(' exprlist ')'
+    | ;
 
-funcall: Ident paramlist { DEBUG("Function call"); };
+
+fundef: KeyFun Ident paramlist '{' statementlist'}' { DEBUG("Function");};
+
+paramlist: paramlist '(' params ')'
+         |  paramlist '(' ')'
+         | '(' params ')'
+         | '(' ')';
+
+params: IOqualifyier paramdecl ',' params
+      | IOqualifyier paramdecl;
+
+IOqualifyier: KeyIn
+            | KeyOut
+            | KeyIn KeyOut
+            | KeyOut KeyIn
+            | ;
+
+paramdecl: type ':' Ident { DEBUG("Param-Declaration"); };
+
+funcall: Ident argumentlist { DEBUG("Function call"); };
+
+assign: Ident '=' expr { DEBUG("Assignment"); };
+
+moduleimport: KeyImport ValStr { DEBUG("Module-Import"); };
 
 statementlist: statement statementlist
     | statement;
@@ -86,6 +110,7 @@ statementlist: statement statementlist
 statement: assign
         | decl
         | definition
+        | while
         | branch
         | funcall;
 
@@ -99,6 +124,8 @@ branchelseifs: branchelseifs branchelseif
 branch: branchif branchelseifs
     | branchif branchelseifs branchelse;
 
+while: KeyWhile expr '{' statementlist '}' { DEBUG("while"); };
+
 identlist: Ident ',' identlist
         | Ident;