Parse simple number literal

src/main.rs

@@ -1,9 +1,11 @@
 use std::fs;
 use std::path::PathBuf;
 
+use chumsky::Parser as _;
 use clap::Parser;
 
 mod builtin;
+mod parser;
 mod table;
 mod value;
 
@@ -25,9 +27,14 @@ fn main() -> anyhow::Result<()> {
     match args.command {
         Command::Parse { file } => {
             let content = fs::read_to_string(&file)?;
-            print!("{content}");
-            if !content.ends_with('\n') {
-                println!();
+            match parser::parser().parse(&content as &str) {
+                Ok(lit) => println!("Successful parse: {lit:#?}"),
+                Err(errs) => {
+                    println!("Parsing failed");
+                    for err in errs {
+                        println!("{err:?}");
+                    }
+                }
             }
         }
     }

src/parser.rs

@@ -0,0 +1,37 @@
+use chumsky::prelude::*;
+
+#[derive(Debug)]
+pub enum Lit {
+    Num(i64),
+}
+
+fn lit_num() -> impl Parser<char, i64, Error = Simple<char>> {
+    let sign = just('+')
+        .or(just('-'))
+        .or_not()
+        .map(|s| if s == Some('-') { -1_i128 } else { 1_i128 });
+
+    let digits = text::int(10);
+
+    sign.then(digits).try_map(|(sign, digits), span| {
+        // u64::MIN and u32::MAX have 19 digits in base 10
+        if digits.len() > 19 {
+            return Err(Simple::custom(span, "number out of range"));
+        }
+
+        let number = sign * digits.parse::<i128>().unwrap();
+        if number < i64::MIN.into() || number > u64::MAX.into() {
+            return Err(Simple::custom(span, "number out of range"));
+        }
+
+        Ok(number as i64)
+    })
+}
+
+fn lit() -> impl Parser<char, Lit, Error = Simple<char>> {
+    lit_num().map(Lit::Num)
+}
+
+pub fn parser() -> impl Parser<char, Lit, Error = Simple<char>> {
+    lit().padded().then_ignore(end())
+}