Implement function parsing

With a lot of dummy code, especially around expression parsing

src/parser.rs

@@ -39,7 +39,7 @@ pub struct ParseError {
 }
 
 impl ParseError {
-    fn new<T>(msg: &str) -> ParseResult<T> {
+    fn result_from_str<T>(msg: &str) -> ParseResult<T> {
         Err(ParseError { msg: msg.to_string() })
     }
 }
@@ -49,11 +49,12 @@ impl ParseError {
    delimiter := Newline | Semicolon
    statement := declaration | expression
    declaraion :=  Fn prototype expression
-   prototype := identifier LParen (Ident Comma?)* RParen
+   prototype := identifier LParen identlist RParen
+   identlist := Ident (Comma Ident)*
    expression := primary_expression (op primary_expression)*
    primary_expression :=  Variable | Number | String | call_expr | paren_expr
    paren_expr := LParen expression RParen
-   call_expr := identifier LParen (expression Comma ?)* RParen
+   call_expr := identifier LParen identlist RParen
    op := '+', '-', etc.
  */
 
@@ -85,22 +86,72 @@ pub fn parse(tokens: &[Token], parsed_tree: &[ASTNode]) -> ParseResult<AST> {
     Ok(ast)
 }
 
+macro_rules! expect {
+    ($token:pat, $tokens:expr, $error:expr) => {
+        match $tokens.pop() {
+            Some($token) => (),
+            _ => return ParseError::result_from_str($error)
+        };
+    }
+}
+
 fn parse_statement(tokens: &mut Vec<Token>) -> ParseResult<ASTNode> {
     use tokenizer::Token::*;
     let cur_tok: Token = tokens.last().unwrap().clone();
-    let result: ASTNode = match cur_tok {
+    let node: ASTNode = match cur_tok {
         Keyword(Kw::Fn) => try!(parse_declaration(tokens)),
         _ => try!(parse_expression(tokens))
     };
 
-    Ok(result)
+    Ok(node)
 }
 
 fn parse_declaration(tokens: &mut Vec<Token>) -> ParseResult<ASTNode> {
+    use tokenizer::Token::*;
+    expect!(Fn, tokens, "Expected 'fn'");
+    let prototype = try!(parse_prototype(tokens));
+    let body = try!(parse_body(tokens));
+    Ok(ASTNode::FuncNode(Function { prototype: prototype, body: body}))
+}
+
+fn parse_prototype(tokens: &mut Vec<Token>) -> ParseResult<Prototype> {
+    use tokenizer::Token::*;
+    let name: String = match tokens.pop() {
+        Some(Identifier(name)) => name,
+        _ => return ParseError::result_from_str("Expected identifier")
+    };
+    expect!(LParen, tokens, "Expected '('");
+    let mut args: Vec<String> = try!(parse_identlist(tokens));
+    expect!(RParen, tokens, "Expected ')'");
+
+    Ok(Prototype {name: name, args: args})
+}
+
+fn parse_identlist(tokens: &mut Vec<Token>) -> ParseResult<Vec<String>> {
+    use tokenizer::Token::*;
+    let mut args: Vec<String> = Vec::new();
+    loop {
+        match tokens.pop() {
+            Some(Identifier(name)) => {
+                args.push(name);
+                if let Some(&Comma) = tokens.last() {
+                    tokens.pop();
+                } else {
+                    break;
+                }
+            },
+
+            _ => break
+        }
+    }
+
+    Ok(args)
+}
+
+fn parse_body(tokens: &mut Vec<Token>) -> ParseResult<Expression> {
     use tokenizer::Token::*;
     tokens.pop();
-    tokens.pop();
-    Ok(ASTNode::ExprNode(Expression::StringLiteral("Declaration".to_string())))
+    Ok(Expression::Number(101.01))
 }
 
 fn parse_expression(tokens: &mut Vec<Token>) -> ParseResult<ASTNode> {