fastc 0.1.0

A safe C-like language that compiles to C11
Documentation 
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//! Parser for FastC

mod decl;
mod expr;
mod stmt;
mod types;

use crate::ast::File;
use crate::diag::CompileError;
use crate::lexer::{Span, Spanned, Token};

/// Parser state
pub struct Parser<'a> {
    tokens: &'a [Spanned<Token>],
    pos: usize,
    source: &'a str,
    filename: &'a str,
}

impl<'a> Parser<'a> {
    /// Create a new parser
    pub fn new(tokens: &'a [Spanned<Token>], source: &'a str, filename: &'a str) -> Self {
        Self {
            tokens,
            pos: 0,
            source,
            filename,
        }
    }

    /// Parse a complete file
    pub fn parse_file(&mut self) -> Result<File, CompileError> {
        let mut items = Vec::new();

        while !self.is_at_end() {
            items.push(self.parse_item()?);
        }

        Ok(File { items })
    }

    // Token access helpers

    fn current(&self) -> &Token {
        &self.tokens.get(self.pos).map(|t| &t.node).unwrap_or(&Token::Eof)
    }

    fn current_span(&self) -> Span {
        self.tokens
            .get(self.pos)
            .map(|t| t.span.clone())
            .unwrap_or(self.source.len()..self.source.len())
    }

    fn peek(&self) -> &Token {
        self.tokens
            .get(self.pos + 1)
            .map(|t| &t.node)
            .unwrap_or(&Token::Eof)
    }

    fn advance(&mut self) -> &Token {
        if !self.is_at_end() {
            self.pos += 1;
        }
        self.previous()
    }

    fn previous(&self) -> &Token {
        &self.tokens[self.pos.saturating_sub(1)].node
    }

    fn previous_span(&self) -> Span {
        self.tokens[self.pos.saturating_sub(1)].span.clone()
    }

    fn is_at_end(&self) -> bool {
        matches!(self.current(), Token::Eof)
    }

    fn check(&self, token: &Token) -> bool {
        std::mem::discriminant(self.current()) == std::mem::discriminant(token)
    }

    fn consume(&mut self, expected: &Token, message: &str) -> Result<(), CompileError> {
        if self.check(expected) {
            self.advance();
            Ok(())
        } else {
            Err(self.error(message))
        }
    }

    fn error(&self, message: &str) -> CompileError {
        CompileError::parse(message, self.current_span(), self.source)
    }

    fn expect_ident(&mut self) -> Result<String, CompileError> {
        match self.current().clone() {
            Token::Ident(name) => {
                self.advance();
                Ok(name)
            }
            _ => Err(self.error("expected identifier")),
        }
    }
}