sybil/src/syn/peg.rs

use crate::obj::prelude::{Float, Int, Str};
use crate::syn::ast::*;
use crate::syn::span::*;
use pest::{error::Error, iterators::Pair, Parser};
use std::rc::Rc;

#[derive(pest_derive::Parser)]
#[grammar = "syn/parser.pest"]
pub struct SybilParser;

pub type Result<T, E = Error<Rule>> = std::result::Result<T, E>;

fn unescape_string(text: &str) -> Str {
    let mut string = String::with_capacity(text.len() - 2);
    let mut chars = text.chars().skip(1).take(text.len() - 2);
    while let Some(c) = chars.next() {
        if c == '\\' {
            let c = match chars
                .next()
                .expect("reached end of string literal before escape")
            {
                '"' => '"',
                '\'' => '\'',
                '\\' => '\\',
                'n' => '\n',
                'r' => '\r',
                't' => '\t',
                u => panic!(
                    "unexpected character escape that made it through the lexer: {:?}",
                    u
                ),
            };
            string.push(c);
        } else {
            string.push(c);
        }
    }
    string
}

fn parse_atom(source: &Rc<String>, pair: Pair<Rule>) -> Result<SpAtom> {
    let pair_span = pair.as_span();
    let atom = match pair.as_rule() {
        Rule::float => {
            let float = pair.as_str().parse::<Float>().unwrap();
            Atom::Float(float)
        }
        Rule::int => {
            let int = pair.as_str().parse::<Int>().unwrap();
            Atom::Int(int)
        }
        Rule::assign => {
            let word = pair.into_inner().next().unwrap().as_str().to_string();
            Atom::Assign(word)
        }
        Rule::word => {
            let word = pair.as_str().to_string();
            Atom::Word(word)
        }
        Rule::str => {
            let string = pair.as_str();
            Atom::Str(unescape_string(string))
        }
        Rule::apply => Atom::Apply,
        rule => unreachable!("{:?}", rule),
    };
    let span = Span {
        source: Rc::clone(source),
        start: pair_span.start(),
        end: pair_span.end(),
    };
    Ok(SpAtom::new(span, atom))
}

fn parse_expr(source: &Rc<String>, pair: Pair<Rule>) -> Result<SpExpr> {
    let pair_span = pair.as_span();
    let expr = match pair.as_rule() {
        Rule::atom => Expr::Atom(parse_atom(source, pair.into_inner().next().unwrap())?),
        Rule::quote => Expr::Quote(
            pair.into_inner()
                .map(|pair| parse_stmt(source, pair.into_inner().next().unwrap()))
                .collect::<Result<Vec<_>>>()?,
        ),
        rule => unreachable!("{:?}", rule),
    };
    let span = Span {
        source: Rc::clone(source),
        start: pair_span.start(),
        end: pair_span.end(),
    };
    Ok(SpExpr::new(span, expr))
}

fn parse_stmt(source: &Rc<String>, pair: Pair<Rule>) -> Result<SpStmt> {
    let pair_span = pair.as_span();
    let stmt = match pair.as_rule() {
        Rule::expr => Stmt::Expr(parse_expr(source, pair.into_inner().next().unwrap())?),
        rule => unreachable!("{:?}", rule),
    };
    let span = Span {
        source: Rc::clone(&source),
        start: pair_span.start(),
        end: pair_span.end(),
    };
    Ok(SpStmt::new(span, stmt))
}

pub fn parse_file(source: impl ToString, text: &str) -> Result<Vec<SpStmt>> {
    let input = SybilParser::parse(Rule::file, text)?.next().unwrap();
    let source = Rc::new(source.to_string());
    let mut stmts = Vec::new();
    for pair in input.into_inner() {
        match pair.as_rule() {
            Rule::EOI => {}
            Rule::stmt => {
                let pair = pair.into_inner().next().unwrap();
                stmts.push(parse_stmt(&source, pair)?);
            }
            rule => unreachable!("{:?}", rule),
        }
    }
    Ok(stmts)
}