schala/schala-lang/language/src/parser.rs

extern crate nom;

use std::rc::Rc;
use std::str::FromStr;

use nom::IResult;
use nom::character::complete::{one_of, space0, alphanumeric0};
use nom::bytes::complete::{tag, take, take_while, take_while1, take_until};
use nom::combinator::{map, map_res, value, opt, verify};
use nom::multi::{separated_list, separated_nonempty_list, many1, many0};
use nom::error::{context, VerboseError};
use nom::branch::alt;
use nom::sequence::{pair, delimited, preceded};

use crate::ast::*;
use crate::builtin::Builtin;

type ParseResult<'a, T> = IResult<&'a str, T, VerboseError<&'a str>>;


fn single_alphabetic_character(text: &str) -> ParseResult<char> {
  let p = verify(take(1usize), |s: &str| s.chars().nth(0).map(|c| c.is_alphabetic()).unwrap_or(false));
  map(p, |s: &str| s.chars().nth(0).unwrap())(text)
}

fn single_alphanumeric_character(text: &str) -> ParseResult<char> {
  let p = verify(take(1usize), |s: &str| s.chars().nth(0).map(|c| c.is_alphanumeric() || c == '_').unwrap_or(false));
  map(p, |s: &str| s.chars().nth(0).unwrap())(text)
}

fn identifier(text: &str) -> ParseResult<Rc<String>> {
  use nom::character::complete::char;
  map(alt((
    pair(char('_'), many1(single_alphanumeric_character)),
    pair(single_alphabetic_character, many0(single_alphanumeric_character))
  )),
  |(first, rest): (char, Vec<char>)| Rc::new(format!("{}{}", first, rest.into_iter().collect::<String>()))
  )(text)
}

const OPERATOR_CHARS: &'static str = "~`!@#$%^&*-+=<>?/|";
fn parse_binop(text: &str) -> ParseResult<BinOp> {
  let (text, op): (_, Vec<char>) = context("Binop", many1(one_of(OPERATOR_CHARS)))(text)?;
  let sigil: String = op.into_iter().collect();
  Ok((text, BinOp::from_sigil(&sigil)))
}

fn bool_literal(text: &str) -> ParseResult<ExpressionKind> {
  let p = alt((
    value(true, tag("true")),
    value(false, tag("false"))
  ));
  map(p, ExpressionKind::BoolLiteral)(text)
}

fn number_literal(text: &str) -> ParseResult<ExpressionKind> {
  let num_lit = many1(alt((
    map(one_of("1234567890"), |s: char| Some(s)),
    map(nom::character::complete::char('_'), |_| None)
  )));

  let (text, n) = map_res(num_lit,
    |digits: Vec<Option<char>>| {
      let num_str: String = digits.into_iter().filter_map(|x| x).collect();
      u64::from_str_radix(&num_str, 10)
    })(text)?;

  Ok((text, ExpressionKind::NatLiteral(n)))
}


fn binary_literal(input: &str) -> ParseResult<ExpressionKind> {
  let p = preceded(tag("0b"), take_while1(|c: char| c == '0' || c == '1'));
  let (rest, n): (&str, u64) = map_res(
    p, |hex_str: &str| u64::from_str_radix(hex_str, 2)
  )(input)?;
  let expr = ExpressionKind::NatLiteral(n);
  Ok((rest, expr))
}

fn hex_literal(input: &str) -> ParseResult<ExpressionKind> {
  let p = preceded(tag("0x"), take_while1(|c: char| c.is_digit(16)));
  let (rest, n): (&str, u64) = map_res(
    p, |hex_str: &str| u64::from_str_radix(hex_str, 16)
  )(input)?;
  let expr = ExpressionKind::NatLiteral(n);
  Ok((rest, expr))
}

fn string_literal(text: &str) -> ParseResult<ExpressionKind> {
  use nom::character::complete::char;
  let (text, string_output) = delimited(
    char('"'), take_until("\""), char('"')
  )(text)?;
  let expr = ExpressionKind::StringLiteral(Rc::new(string_output.to_string()));
  Ok((text, expr))
}

fn literal(input: &str) -> ParseResult<ExpressionKind> {
  alt((
    string_literal,
    hex_literal,
    binary_literal,
    number_literal,
    bool_literal
  ))(input)
}

fn paren_expr(text: &str) -> ParseResult<ExpressionKind> {
  use nom::character::complete::char;
  context("Paren expression", delimited(char('('), expression_kind, char(')')))(text)
}

fn prefix_op(input: &str) -> ParseResult<PrefixOp> {
  use nom::character::complete::char;
  let p = alt((char('+'), char('-'), char('!')));
  map(p, |sigil| PrefixOp::from_str(&sigil.to_string()).unwrap())(input)
}

fn identifier_expr(text: &str) -> ParseResult<ExpressionKind> {
  let (text, qualified_identifier) = map(
    qualified_identifier_list,
    |components| QualifiedName { id: ItemId::new(0), components }
  )(text)?;
  //TODO handle struct literals
  let exp = Expression::new(ItemId::new(0), ExpressionKind::Value(qualified_identifier));
  Ok((text, exp.kind))
}

fn qualified_identifier_list(text: &str) -> ParseResult<Vec<Rc<String>>> {
  separated_nonempty_list(tag("::"), identifier)(text)
}

fn primary_expr(text: &str) -> ParseResult<ExpressionKind> {
  // primary := literal | paren_expr | if_expr | for_expr | while_expr | identifier_expr | lambda_expr | anonymous_struct | list_expr

  alt((
    literal,
    paren_expr,
    identifier_expr,
  ))(text)
}

fn invocation_argument(text: &str) -> ParseResult<InvocationArgument> {
  use nom::character::complete::char;
  alt((
    value(InvocationArgument::Ignored, pair(char('_'), alphanumeric0)),
    map(expression_kind, |kind: ExpressionKind| InvocationArgument::Positional(
        Expression {  id: ItemId::new(0), kind, type_anno: None }))
    //map(identifier, |id: Rc<String>| 
  ))(text)
}

fn call_expr(text: &str) -> ParseResult<ExpressionKind> {
  use nom::character::complete::char;
  let (text, expr) = primary_expr(text)?;
  let (text, call_part) = opt(
    delimited(char('('), separated_list(char(','), invocation_argument), char(')'))
  )(text)?;
  let output = if let Some(arguments) = call_part {
    let f = bx!(Expression { id: ItemId::new(0), kind: expr, type_anno: None }); 
    ExpressionKind::Call { f, arguments }
  } else {
    expr
  };
  Ok((text, output))
}

fn prefix_expr(text: &str) -> ParseResult<ExpressionKind> {
  let (text, pfx) = delimited(space0, opt(prefix_op), space0)(text)?;
  let (text, result) = call_expr(text)?;
  match pfx {
    None => Ok((text, result)),
    Some(pfx) => {
      let exp = Expression { id: ItemId::new(0), kind: result, type_anno: None }; 
      Ok((text, ExpressionKind::PrefixExp(pfx, Box::new(exp))))
    }
  }
}

// this implements Pratt parsing, see http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/
fn precedence_expr(text: &str) -> ParseResult<ExpressionKind> {
  fn inner_precedence_expr(input: &str, precedence: i32) -> ParseResult<ExpressionKind> {
    let (mut outer_rest, mut lhs) = prefix_expr(input)?;
    loop {
      let (rest, _) = space0(outer_rest)?;
      let (rest, maybe_binop) = opt(parse_binop)(rest)?;
      let (new_precedence, binop) = match maybe_binop {
        Some(binop) => (binop.precedence(), binop),
        None => break,
      };

      if precedence >= new_precedence {
        break;
      }
      let (rest, _) = space0(rest)?;
      let (rest, rhs) = inner_precedence_expr(rest, new_precedence)?;
      outer_rest = rest;
      lhs = ExpressionKind::BinExp(binop,
        bx!(Expression::new(ItemId::new(0), lhs)),
        bx!(Expression::new(ItemId::new(0), rhs))
      );
    }
    Ok((outer_rest, lhs))
  }
  context("Precedence expression",
    |input| inner_precedence_expr(input, BinOp::min_precedence())
  )(text)
}

fn expression_kind(text: &str) -> ParseResult<ExpressionKind> {
  precedence_expr(text)
}

pub fn perform_parsing(input: &str) -> Result<String, String> {
  let output = match expression_kind(input) {
    Ok((rest, ast)) => format!("{:?} (rest: {})", ast, rest),
    Err(nom::Err::Incomplete(needed)) => format!("Incomplete: {:?}" ,needed),
    Err(nom::Err::Error(verbose_error) | nom::Err::Failure(verbose_error)) => {
      format!("Verbose Error: ` {:?} `", verbose_error)
      //nom::error::convert_error(input, verbose_error)
    }
  };
      
  Ok(output)
}