From c6b0f7d7d1cb0f38b680a69811ca2ae667d59e40 Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Thu, 13 Feb 2020 02:48:38 -0800
Subject: [PATCH] Pratt parsing

---
 schala-lang/language/src/ast/operators.rs |  4 ++
 schala-lang/language/src/parser.rs        | 61 ++++++++++++++++++-----
 2 files changed, 52 insertions(+), 13 deletions(-)

diff --git a/schala-lang/language/src/ast/operators.rs b/schala-lang/language/src/ast/operators.rs
index 0e3f2b0..78030a6 100644
--- a/schala-lang/language/src/ast/operators.rs
+++ b/schala-lang/language/src/ast/operators.rs
@@ -68,6 +68,10 @@ impl BinOp {
     let s = token_kind_to_sigil(op_tok)?;
     Some(binop_precedences(s))
   }
+
+  pub fn precedence(&self) -> i32 {
+    binop_precedences(self.sigil.as_str())
+  }
 }
 
 fn token_kind_to_sigil<'a>(tok: &'a TokenKind) -> Option<&'a str> {
diff --git a/schala-lang/language/src/parser.rs b/schala-lang/language/src/parser.rs
index fef059d..5dac49b 100644
--- a/schala-lang/language/src/parser.rs
+++ b/schala-lang/language/src/parser.rs
@@ -4,28 +4,21 @@ use std::rc::Rc;
 use std::str::FromStr;
 
 use nom::IResult;
+use nom::character::complete::{one_of};
 use nom::bytes::complete::{tag, take_while};
-use nom::combinator::{map_res, value, opt};
+use nom::combinator::{map, map_res, value, opt};
 use nom::multi::many1;
-//use nom::error::{ParseError, ErrorKind};
+use nom::error::{ParseError, ErrorKind};
 use nom::branch::alt;
+use nom::sequence::delimited;
 
 use crate::ast::*;
 use crate::builtin::Builtin;
 
 
-/*
-#[derive(Debug, Clone)]
-enum Prefix {
-  Plus,
-  Minus,
-  Bang,
-}
-*/
-
 const OPERATOR_CHARS: &'static str = "~`!@#$%^&*-+=<>?/|";
 
-fn parse_operator(input: &str) -> IResult<&str, BinOp> {
+fn parse_binop(input: &str) -> IResult<&str, BinOp> {
   use nom::character::complete::one_of;
   let (rest, op): (_, Vec<char>) = many1(one_of(OPERATOR_CHARS))(input)?;
   let sigil: String = op.into_iter().collect();
@@ -41,6 +34,22 @@ fn parse_bool_literal(input: &str) -> IResult<&str, ExpressionKind> {
   Ok((rest, ExpressionKind::BoolLiteral(value)))
 }
 
+fn parse_number_literal(input: &str) -> IResult<&str, ExpressionKind> {
+  let num_lit = many1(alt((
+    map(one_of("1234567890"), |s: char| Some(s)),
+    map(nom::character::complete::char('_'), |_| None)
+  )));
+
+  let (rest, 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)
+    })(input)?;
+
+  Ok((rest, ExpressionKind::NatLiteral(n)))
+}
+
+
 fn parse_binary_literal(input: &str) -> IResult<&str, ExpressionKind> {
   let (rest, _) = tag("0b")(input)?;
   let (rest, n): (&str, u64) = map_res(
@@ -72,6 +81,7 @@ fn parse_string_literal(input: &str) -> IResult<&str, ExpressionKind> {
 fn parse_literal(input: &str) -> IResult<&str, ExpressionKind> {
   alt((
     parse_string_literal,
+    parse_number_literal,
     parse_hex_literal,
     parse_binary_literal,
     parse_bool_literal
@@ -119,8 +129,33 @@ fn prefix_expr(input: &str) -> IResult<&str, ExpressionKind> {
   }
 }
 
+// this implements Pratt parsing, see http://journal.stuffwithstuff.com/2011/03/19/pratt-parsers-expression-parsing-made-easy/
+fn precedence_expr(input: &str, precedence: i32) -> IResult<&str, ExpressionKind>  {
+  let (mut outer_rest, mut lhs) = prefix_expr(input)?;
+  loop {
+    let (rest, maybe_binop) = opt(parse_binop)(outer_rest)?;
+    println!("REST: {} | and maybe: {:?}", rest, maybe_binop);
+    let (new_precedence, binop) = match maybe_binop {
+      Some(binop) => (binop.precedence(), binop),
+      None => break,
+    };
+    println!("Calculated new precedence: {} for binop: {:?}", new_precedence, binop);
+
+    if precedence >= new_precedence {
+      break;
+    }
+    let (rest, rhs) = 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))
+}
+
 fn expression_kind(input: &str) -> IResult<&str, ExpressionKind> {
-  prefix_expr(input)
+  precedence_expr(input, BinOp::min_precedence())
 }
 
 pub fn perform_parsing(input: &str) -> Result<String, String> {