Preliminary addition of function blocks

Grammar

@@ -7,6 +7,12 @@
 
 <statement> := let <id> = <expr>
             |  <expr>
+            | <fn_block>
+
+<fn_block> := fn <id> ( <arg_list> ) <statements> end
+
+<arg_list> := e
+           | <id> , <arg_list>
 
 <expr> := if <expr> then <statements> end
        |  if <expr> then <statements> else <statements> end

src/parser.rs

@@ -15,6 +15,7 @@ pub enum AST {
     Statements(Vec<AST>),
     IfStatement(Box<AST>, Box<AST>, Option<Box<AST>>),
     WhileStatement(Box<AST>, Box<AST>),
+    Function(Vec<String>, Box<AST>),
     DoNothing
 }
 
@@ -105,10 +106,18 @@ fn statements(tokens: &mut Tokens) -> ParseResult {
 fn statement(tokens: &mut Tokens) -> ParseResult {
     match tokens.peek().map(|i| i.clone()) {
         Some(&Keyword(Kw::Let)) => let_expression(tokens),
+        Some(&Keyword(Kw::Fn)) => function_block(tokens),
         _ => expression(tokens)
     }
 }
 
+fn function_block(tokens: &mut Tokens) -> ParseResult {
+    expect!(Keyword(Kw::Fn), tokens);
+    expect!(Keyword(Kw::End), tokens);
+
+    Ok(AST::Function(Vec::new(), Box::new(AST::DoNothing)))
+}
+
 fn let_expression(tokens: &mut Tokens) -> ParseResult {
     expect!(Keyword(Kw::Let), tokens);
     if let Some(&Identifier(ref name)) = tokens.next() {