Convert parsing to method-based

src/parser.rs

@@ -58,23 +58,48 @@ impl ParseError {
    op := '+', '-', etc.
  */
 
-pub fn parse(tokens: &[Token], parsed_tree: &[ASTNode]) -> ParseResult<AST> {
+struct Parser {
+    tokens: Vec<Token>,
+}
+
+impl Parser {
+    fn initialize(tokens: &[Token]) -> Parser {
+        let mut tokens = tokens.to_vec();
+        tokens.reverse();
+        Parser { tokens: tokens }
+    }
+
+    fn peek(&mut self) -> Option<Token> {
+        self.tokens.last().map(|x| x.clone())
+    }
+
+    fn next(&mut self) {
+        self.tokens.pop();
+    }
+}
+
+macro_rules! expect {
+    ($self_:expr, $token:pat, $error:expr) => {
+        match $self_.peek() {
+            Some($token) => {$self_.next();},
+            _ => return ParseError::result_from_str($error)
+        }
+    }
+}
+
+impl Parser {
+    fn program(&mut self) -> ParseResult<AST> {
         use tokenizer::Token::*;
-
-    let mut rest: Vec<Token> = tokens.to_vec();
-    rest.reverse();
-
-    let mut ast = parsed_tree.to_vec();
-
+        let mut ast = Vec::new(); //TODO have this come from previously-parsed tree
         loop {
-        let cur_tok = match rest.last() {
+            let cur_tok = match self.peek() {
                 Some(t) => t.clone(),
                 None => break
             };
 
             let result: ParseResult<ASTNode> = match cur_tok {
-            Newline | Semicolon => { rest.pop(); continue},
-            _ => parse_statement(&mut rest)
+                Newline | Semicolon => { self.next(); continue},
+                _ => self.statement()
             };
 
             match result {
@@ -84,58 +109,49 @@ 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> {
+    fn statement(&mut self) -> ParseResult<ASTNode> {
         use tokenizer::Token::*;
-    let cur_tok: Token = tokens.last().unwrap().clone();
+        let cur_tok: Token = self.peek().unwrap().clone();
         let node: ASTNode = match cur_tok {
-        Keyword(Kw::Fn) => try!(parse_declaration(tokens)),
-        _ => try!(parse_expression(tokens))
+            Keyword(Kw::Fn) => try!(self.declaration()),
+            _ => try!(self.expression())
         };
 
         Ok(node)
-}
+    }
 
-fn parse_declaration(tokens: &mut Vec<Token>) -> ParseResult<ASTNode> {
+    fn declaration(&mut self) -> ParseResult<ASTNode> {
         use tokenizer::Token::*;
-    expect!(Fn, tokens, "Expected 'fn'");
-    let prototype = try!(parse_prototype(tokens));
-    let body = try!(parse_body(tokens));
+        expect!(self, Fn, "Expected 'fn'");
+        let prototype = try!(self.prototype());
+        let body = try!(self.body());
         Ok(ASTNode::FuncNode(Function { prototype: prototype, body: body}))
-}
+    }
 
-fn parse_prototype(tokens: &mut Vec<Token>) -> ParseResult<Prototype> {
+    fn prototype(&mut self) -> ParseResult<Prototype> {
         use tokenizer::Token::*;
-    let name: String = match tokens.pop() {
-        Some(Identifier(name)) => name,
+        let name: String = match self.peek() {
+            Some(Identifier(name)) => {self.next(); 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 ')'");
-
+        expect!(self, LParen, "Expected '('");
+        let mut args: Vec<String> = try!(self.identlist());
+        expect!(self, RParen, "Expected ')'");
         Ok(Prototype {name: name, args: args})
-}
+    }
 
-fn parse_identlist(tokens: &mut Vec<Token>) -> ParseResult<Vec<String>> {
+    fn identlist(&mut self) -> ParseResult<Vec<String>> {
         use tokenizer::Token::*;
         let mut args: Vec<String> = Vec::new();
         loop {
-        match tokens.pop() {
+            match self.peek() {
                 Some(Identifier(name)) => {
                     args.push(name);
-                if let Some(&Comma) = tokens.last() {
-                    tokens.pop();
+                    self.next();
+                    if let Some(Comma) = self.peek() {
+                        self.next();
                     } else {
                         break;
                     }
@@ -146,17 +162,23 @@ fn parse_identlist(tokens: &mut Vec<Token>) -> ParseResult<Vec<String>> {
         }
 
         Ok(args)
-}
+    }
 
-fn parse_body(tokens: &mut Vec<Token>) -> ParseResult<Expression> {
+    fn body(&mut self) -> ParseResult<Expression> {
         use tokenizer::Token::*;
-    tokens.pop();
+        self.next();
         Ok(Expression::Number(101.01))
-}
+    }
 
-fn parse_expression(tokens: &mut Vec<Token>) -> ParseResult<ASTNode> {
+    fn expression(&mut self) -> ParseResult<ASTNode> {
         use tokenizer::Token::*;
-    tokens.pop();
+        self.next();
         Ok(ASTNode::ExprNode(Expression::StringLiteral("Expr".to_string())))
+    }
+}
+
+pub fn parse(tokens: &[Token], _parsed_tree: &[ASTNode]) -> ParseResult<AST> {
+    let mut parser = Parser::initialize(tokens);
+    parser.program()
 }