Pick this up again, dust it off, get some stuff connected.

Cargo.toml

@@ -13,9 +13,11 @@ name = "ngrc"
 path = "src/bin.rs"
 
 [dependencies]
-lalrpop-util = "0.19.0"
-lazy_static = "1.4.0"
-logos = "0.11.4"
+clap = { version = "^3.0.14", features = ["derive"] }
+lalrpop-util = "^0.19.7"
+lazy_static = "^1.4.0"
+logos = "^0.12.0"
+thiserror = "^1.0.30"
 
 [build-dependencies]
-lalrpop = "0.19.0"
+lalrpop = "^0.19.7"

examples/basic/test1.ngr

@@ -0,0 +1,4 @@
+x = 5;
+y = 4*x + 3;
+print x;
+print y;

src/bin.rs

@@ -1,3 +1,29 @@
-fn main() {
-    println!("Hello, world!");
+use clap::Parser;
+use ngr::syntax::{ParserError, Program};
+
+#[derive(Parser, Debug)]
+#[clap(author, version, about, long_about = None)]
+struct CommandLineArguments {
+    /// Optional output file name
+    #[clap(short, long)]
+    output: Option<String>,
+
+    /// The file to parse
+    file: String
+}
+
+fn real_main() -> Result<(), ParserError> {
+    let args = CommandLineArguments::parse();
+
+    let program = Program::from_file(&args.file)?;
+    println!("args: {:?}", args);
+    println!("program: {:?}", program);
+
+    Ok(())
+}
+
+fn main() {
+    if let Err(e) = real_main() {
+        println!("{}", e);
+    }
 }

src/syntax.rs

@@ -12,16 +12,62 @@ use crate::syntax::tokens::Token;
 #[cfg(test)]
 use crate::util::istring::InternedString;
 use lalrpop_util::ParseError;
+use std::fmt;
 use std::fs;
 use std::io;
 use std::str::FromStr;
+use thiserror::Error;
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum ParserError {
     IOError(io::Error),
     ParseError(ParseError<Location, Token, LexerError>),
 }
 
+impl fmt::Display for ParserError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            ParserError::IOError(e) => write!(f, "IO error: {}", e),
+
+            ParserError::ParseError(ParseError::ExtraToken{ token: (loc, tok, _)}) => {
+                write!(f, "{}: Unexpected additional token ({}) found at end of file", loc, tok) 
+            }
+            ParserError::ParseError(ParseError::InvalidToken { location }) => {
+                write!(f, "{}: Unexpected token encountered", location)
+            }
+            ParserError::ParseError(ParseError::UnrecognizedEOF { location, expected }) => {
+                write!(f, "{}: Unexpected EOF{}", location, display_expected(expected))
+            }
+            ParserError::ParseError(ParseError::UnrecognizedToken { token: (location, tok, _), expected }) => {
+                write!(f, "{}: Unexpected token {}{}", location, tok, display_expected(expected))
+            }
+            ParserError::ParseError(ParseError::User{ error }) => {
+                write!(f, "{}: Couldn't process input (lexer error)", error.location)
+            }
+        }
+    }
+}
+
+fn display_expected(expected: &Vec<String>) -> String {
+    match expected.len() {
+        0 => "".to_string(),
+        1 => format!("; expected {}", expected[0]),
+        2 => format!("; expected {} or {}", expected[0], expected[1]),
+        n => format!("; expected {}or {}", comma_separate(&expected[0..n-1]), expected[n-1])
+    }
+}
+
+fn comma_separate(strings: &[String]) -> String {
+    let mut result = String::new();
+
+    for s in strings.iter() {
+        result.push_str(&s);
+        result.push_str(", ");
+    }
+
+    result
+}
+
 impl From<io::Error> for ParserError {
     fn from(x: io::Error) -> Self {
         ParserError::IOError(x)

src/syntax/token_stream.rs

@@ -1,6 +1,7 @@
 use crate::syntax::tokens::Token;
 use crate::util::istring::InternedString;
 use logos::{Logos, SpannedIter};
+use std::fmt;
 use std::fs::File;
 use std::io;
 use std::io::Read;
@@ -31,6 +32,15 @@ pub enum Location {
     Manufactured,
 }
 
+impl fmt::Display for Location {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Location::InFile(s, off) => write!(f, "{}:{}", s, off),
+            Location::Manufactured => write!(f, "<manufactured>"),
+        }
+    }
+}
+
 impl Location {
     fn new(filename: InternedString, offset: usize) -> Location {
         Location::InFile(filename, offset)
@@ -45,14 +55,12 @@ impl Default for Location {
 
 #[derive(Debug, PartialEq)]
 pub struct LexerError {
-    filename: InternedString,
-    offset: usize,
+    pub location: Location,
 }
 
-#[cfg(test)]
 impl LexerError {
     fn new(filename: InternedString, offset: usize) -> LexerError {
-        LexerError { filename, offset }
+        LexerError { location: Location::new(filename, offset) }
     }
 }
 
@@ -64,10 +72,7 @@ impl<'s> Iterator for TokenStream<'s> {
     fn next(&mut self) -> Option<Self::Item> {
         match self.lexer.next() {
             None => None,
-            Some((Token::Error, span)) => Some(Err(LexerError {
-                filename: self.filename,
-                offset: span.start,
-            })),
+            Some((Token::Error, span)) => Some(Err(LexerError::new(self.filename, span.start))),
             Some((token, span)) => {
                 let start = Location::new(self.filename, span.start);
                 let end = Location::new(self.filename, span.end);

src/syntax/tokens.rs

@@ -1,18 +1,17 @@
 use crate::util::istring::InternedString;
 use logos::{Lexer, Logos};
+use std::fmt;
 use std::num::ParseIntError;
 
 #[derive(Logos, Clone, Debug, PartialEq)]
 pub enum Token {
-    #[regex(r"[ \t\n\f]+", logos::skip)]
-    #[regex(r"//.*", logos::skip)]
     #[token("=")]
     Equals,
 
     #[token(";")]
     Semi,
 
-    #[regex(r"[+\-*/]", |v| v.slice().chars().nth(0))]
+    #[regex(r"[+\-*/]", |v| v.slice().chars().next())]
     Operator(char),
 
     #[regex(r"0b[01]+", |v| parse_number(Some(2), v))]
@@ -26,9 +25,29 @@ pub enum Token {
     Variable(InternedString),
 
     #[error]
+    #[regex(r"[ \t\r\n\f]+", logos::skip)]
+    #[regex(r"//.*", logos::skip)]
     Error,
 }
 
+impl fmt::Display for Token {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Token::Equals => write!(f, "'='"),
+            Token::Semi => write!(f, "';'"),
+            Token::Operator(c) => write!(f, "'{}'", c),
+            Token::Number((None, v)) => write!(f, "'{}'", v),
+            Token::Number((Some(2), v)) => write!(f, "'0b{:b}'", v),
+            Token::Number((Some(8), v)) => write!(f, "'0o{:o}'", v),
+            Token::Number((Some(10), v)) => write!(f, "'{}'", v),
+            Token::Number((Some(16), v)) => write!(f, "'0x{:x}'", v),
+            Token::Number((Some(b), v)) => write!(f, "Invalidly-based-number<base={},val={}>", b, v),
+            Token::Variable(s) => write!(f, "'{}'", s),
+            Token::Error => write!(f, "<error>"),
+        }
+    }
+}
+
 #[cfg(test)]
 impl Token {
     pub(crate) fn var(s: &str) -> Token {
@@ -36,9 +55,9 @@ impl Token {
     }
 }
 
-fn parse_number<'a, 'src>(
+fn parse_number(
     base: Option<u8>,
-    value: &'a Lexer<'src, Token>,
+    value: &Lexer<Token>,
 ) -> Result<(Option<u8>, i128), ParseIntError> {
     let (radix, strval) = match base {
         None => (10, value.slice()),