sabre/src/parser/mod.rs

use crate::lexer::Keyword;
use crate::lexer::{Token, TokenKind, Value};
use crate::parser::node_type::*;
use std::iter::Peekable;
use std::vec::IntoIter;

mod node_type;

pub struct Parser {
    tokens: Peekable<IntoIter<Token>>,
    peeked: Vec<Token>,
}

impl Parser {
    pub fn new(tokens: Vec<Token>) -> Parser {
        // FIXME: Fiter without collecting?
        let tokens_without_whitespace: Vec<Token> = tokens
            .into_iter()
            .filter(|token| token.kind != TokenKind::Whitespace && token.kind != TokenKind::Comment)
            .collect();
        Parser {
            tokens: tokens_without_whitespace.into_iter().peekable(),
            peeked: vec![],
        }
    }

    pub fn parse(&mut self) -> Result<Program, String> {
        self.parse_program()
    }

    fn next(&mut self) -> Option<Token> {
        if self.peeked.is_empty() {
            self.tokens.next()
        } else {
            self.peeked.pop()
        }
    }

    fn peek(&mut self) -> Option<Token> {
        if let Some(token) = self.next() {
            self.push(Some(token.to_owned()));
            Some(token)
        } else {
            None
        }
    }

    fn drop(&mut self, count: usize) {
        for _ in 0..count {
            self.next();
        }
    }

    fn push(&mut self, token: Option<Token>) {
        if let Some(t) = token {
            self.peeked.push(t);
        }
    }

    fn has_more(&mut self) -> bool {
        !self.peeked.is_empty() || self.tokens.peek().is_some()
    }

    fn next_token(&mut self) -> Token {
        self.next().expect("failed to parse")
    }

    fn match_token(&mut self, token_kind: TokenKind) -> Result<Token, String> {
        match self.next() {
            Some(token) if token.kind == token_kind => Ok(token),
            other => Err(format!(
                "Token {:?} not found, found {:?}",
                token_kind, other
            )),
        }
    }

    fn peek_token(&mut self, token_kind: TokenKind) -> Result<Token, String> {
        match self.peek() {
            Some(token) if token.kind == token_kind => Ok(token),
            other => Err(format!(
                "Token {:?} not found, found {:?}",
                token_kind, other
            )),
        }
    }

    fn match_keyword(&mut self, keyword: Keyword) -> Result<(), String> {
        let token = self.next_token();

        match token.kind {
            TokenKind::Keyword(k) if k == keyword => Ok(()),
            other => Err(format!("Expected SemiColon, found {:?}", other)),
        }
    }

    fn match_identifier(&mut self) -> Result<String, String> {
        match self.next_token().kind {
            TokenKind::Identifier(n) => Ok(n),
            other => Err(format!("Expected Identifier, found {:?}", other)),
        }
    }
}

impl Parser {
    fn parse_program(&mut self) -> Result<Program, String> {
        let mut functions = Vec::new();
        let globals = Vec::new();

        while self.has_more() {
            functions.push(self.parse_function().expect("Failed to parse function"))
        }

        Ok(Program {
            func: functions,
            globals: globals,
        })
    }

    fn parse_function(&mut self) -> Result<Function, String> {
        self.match_keyword(Keyword::Function)?;
        let name = self.match_identifier()?;

        self.match_token(TokenKind::BraceOpen)?;
        self.match_token(TokenKind::BraceClose)?;
        self.match_token(TokenKind::CurlyBracesOpen)?;

        let mut statements = vec![];

        while let Err(_) = self.peek_token(TokenKind::CurlyBracesClose) {
            let statement = self.parse_statement()?;
            println!("{:?}", statement);
            statements.push(statement);
        }

        self.match_token(TokenKind::CurlyBracesClose)?;

        Ok(Function {
            name: name,
            arguments: Vec::new(),
            statements: statements,
        })
    }

    fn parse_statement(&mut self) -> Result<Statement, String> {
        let token = self.next_token();
        println!("parse_statement: {:?}", token);
        match token.kind {
            TokenKind::Keyword(Keyword::Return) => {
                let state = Statement::Return(self.parse_expression()?);
                self.match_token(TokenKind::SemiColon)?;

                Ok(state)
            }
            other => Err(format!("Expected Statement, found {:?}", other)),
        }
    }

    fn parse_expression(&mut self) -> Result<Expression, String> {
        let token = self.next_token();
        match token.kind {
            TokenKind::Literal(Value::Int) => {
                let state = Expression::Int(token.raw.parse::<u32>().map_err(|e| e.to_string())?);
                Ok(state)
            }
            other => Err(format!("Expected Expression, found {:?}", other)),
        }
    }
}

pub fn parse(tokens: Vec<Token>) -> Result<node_type::Program, String> {
    let mut parser = Parser::new(tokens);

    parser.parse()
}