From 7f0f886fb7e1a4c409b78f62be9f8081aa5c6705 Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Thu, 17 Nov 2022 16:52:37 +0100
Subject: [PATCH] Parse positive numeric literals

---
 src/ast.rs    | 10 ++++++---
 src/parser.rs | 58 ++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 62 insertions(+), 6 deletions(-)

diff --git a/src/ast.rs b/src/ast.rs
index 7cc381b..8617d5e 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -1,18 +1,22 @@
 #[derive(Debug, Clone)]
 pub struct Ident(pub String);
 
+/// Positive number literal.
+///
+/// Possible bases are binary, decimal, hexadecimal. Underscores can be inserted
+/// before and after any digit.
 #[derive(Debug, Clone)]
 pub enum NumLit {
     /// - `0b_0001_1011`
-    /// - `-0b10`
+    /// - `0b10`
     Bin(i64, String),
 
     /// - `12_345`
-    /// - `-7`
+    /// - `7`
     Dec(i64, String),
 
     /// - `0x_c0_f3`
-    /// - `-0xB`
+    /// - `0xB`
     Hex(i64, String),
 }
 
diff --git a/src/parser.rs b/src/parser.rs
index 098d1c9..36b8bd0 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,11 +1,63 @@
 use chumsky::prelude::*;
+use chumsky::text::Character;
 
-use crate::ast::Ident;
+use crate::ast::{Ident, NumLit};
 
 fn ident() -> impl Parser<char, Ident, Error = Simple<char>> {
     text::ident().map(Ident)
 }
 
-pub fn parser() -> impl Parser<char, Ident, Error = Simple<char>> {
-    ident().padded().then_ignore(end())
+fn num_lit_radix_digits(
+    radix: u32,
+    max_digits: usize,
+) -> impl Parser<char, (i64, String), Error = Simple<char>> {
+    filter(move |c: &char| c.is_digit(radix) || *c == '_')
+        .repeated()
+        .at_least(1)
+        .try_map(move |chars, span| {
+            let text = chars.iter().copied().collect::<String>();
+            let digits = chars.into_iter().filter(|c| *c != '_').collect::<String>();
+            if digits.len() > max_digits {
+                return Err(Simple::custom(span, "number out of range"));
+            }
+            let number = u64::from_str_radix(&digits, radix).unwrap();
+            if number > i64::MAX as u64 {
+                return Err(Simple::custom(span, "number out of range"));
+            }
+            Ok((number as i64, text))
+        })
+}
+
+fn num_lit_bin_digits() -> impl Parser<char, (i64, String), Error = Simple<char>> {
+    // u64::MAX in binary is 0b_1111111_11111111_11111111_11111111_11111111_11111111_11111111_11111111
+    // 63 digits are necessary to represent the full range.
+    const MAX_BIN_DIGITS: usize = 63;
+
+    just("0b").ignore_then(num_lit_radix_digits(2, MAX_BIN_DIGITS))
+}
+
+fn num_lit_dec_digits() -> impl Parser<char, (i64, String), Error = Simple<char>> {
+    // u64::MAX in decimal is 9_223_372_036_854_775_807
+    // 19 digits are necessary to represent the full range.
+    const MAX_DEC_DIGITS: usize = 19;
+
+    num_lit_radix_digits(10, MAX_DEC_DIGITS)
+}
+
+fn num_lit_hex_digits() -> impl Parser<char, (i64, String), Error = Simple<char>> {
+    // u64::MAX in hexadecimal is 0x_7fff_ffff_ffff_ffff
+    // 16 digits are necessary to represent the full range.
+    const MAX_HEX_DIGITS: usize = 16;
+
+    just("0x").ignore_then(num_lit_radix_digits(16, MAX_HEX_DIGITS))
+}
+
+fn num_lit() -> impl Parser<char, NumLit, Error = Simple<char>> {
+    (num_lit_bin_digits().map(|(num, text)| NumLit::Bin(num, text)))
+        .or(num_lit_hex_digits().map(|(num, text)| NumLit::Hex(num, text)))
+        .or(num_lit_dec_digits().map(|(num, text)| NumLit::Dec(num, text)))
+}
+
+pub fn parser() -> impl Parser<char, NumLit, Error = Simple<char>> {
+    num_lit().padded().then_ignore(end())
 }