Added recoverable parsing of integers.

examples/main_span_expr_custom_err2.rs

+extern crate nom;
+
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{digit1, multispace0},
+    combinator::map,
+    error,
+    sequence::{preceded, tuple},
+    Err,
+};
+
+use nom_locate::LocatedSpan;
+
+type Span<'a> = LocatedSpan<&'a str>;
+
+#[derive(Debug)]
+pub struct Error<'a>(Span<'a>, Option<Span<'a>>, ErrorKind);
+type IResult<'a, I, O, E = Error<'a>> = Result<(I, O), Err<E>>;
+
+impl<'a> error::ParseError<Span<'a>> for Error<'a> {
+    fn from_error_kind(input: Span<'a>, kind: error::ErrorKind) -> Self {
+        Error(input, None, ErrorKind::Nom(kind))
+    }
+
+    fn append(_: Span<'a>, _: error::ErrorKind, other: Self) -> Self {
+        other
+    }
+}
+
+#[derive(Debug)]
+enum ErrorKind {
+    ParseIntError(std::num::ParseIntError),
+    Nom(error::ErrorKind),
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Op {
+    Add,
+    Sub,
+}
+
+type SpanOp<'a> = (Span<'a>, Op);
+
+fn parse_op(i: Span) -> IResult<Span, SpanOp> {
+    alt((
+        map(tag("+"), |s| (s, Op::Add)),
+        map(tag("-"), |s| (s, Op::Sub)),
+    ))(i)
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Expr<'a> {
+    Num(i32),
+    Num64(i64),
+    BinOp(Box<SpanExpr<'a>>, SpanOp<'a>, Box<SpanExpr<'a>>),
+}
+
+type SpanExpr<'a> = (Span<'a>, Expr<'a>);
+
+pub fn parse_i32<'a>(i: Span<'a>) -> IResult<Span<'a>, SpanExpr> {
+    let (i, digits) = digit1(i)?;
+    match digits.fragment.parse() {
+        Ok(int) => Ok((i, (digits, Expr::Num(int)))),
+        Err(e) => Err(Err::Error(Error(
+            i,
+            Some(digits),
+            ErrorKind::ParseIntError(e),
+        ))),
+    }
+}
+
+pub fn parse_i64<'a>(i: Span<'a>) -> IResult<Span<'a>, SpanExpr> {
+    let (i, digits) = digit1(i)?;
+    match digits.fragment.parse() {
+        Ok(int) => Ok((i, (digits, Expr::Num64(int)))),
+        Err(e) => Err(Err::Error(Error(
+            i,
+            Some(digits),
+            ErrorKind::ParseIntError(e),
+        ))),
+    }
+}
+
+fn parse_expr(i: Span) -> IResult<Span, SpanExpr> {
+    alt((
+        map(
+            tuple((
+                alt((parse_i32, parse_i64)),
+                preceded(multispace0, parse_op),
+                parse_expr_ms,
+            )),
+            |(l, op, r)| (i, Expr::BinOp(Box::new(l), op, Box::new(r))),
+        ),
+        parse_i32,
+        parse_i64,
+    ))(i)
+}
+
+fn parse_expr_ms(i: Span) -> IResult<Span, SpanExpr> {
+    preceded(multispace0, parse_expr)(i)
+}
+
+// dumps a Span into a String
+fn dump_span(s: &Span) -> String {
+    format!(
+        "[line :{:?}, col:{:?}, {:?}]",
+        s.line,
+        s.get_column(),
+        s.fragment
+    )
+}
+
+// dumps a SpanExpr into a String
+fn dump_expr(se: &SpanExpr) -> String {
+    let (s, e) = se;
+    match e {
+        Expr::Num(_) => dump_span(s),
+        Expr::Num64(_) => dump_span(s),
+        Expr::BinOp(l, (sop, _), r) => {
+            format!("<{} {} {}>", dump_expr(l), dump_span(sop), dump_expr(r))
+        }
+    }
+}
+
+fn main() {
+    let i = "\n    1+2+10000- \n3";
+    // uncomment below for an error example
+    let i = "\n    1+200000000000000000+a10000- \n3";
+    let pe = parse_expr_ms(Span::new(i));
+    println!("pe: {:?}\n", pe);
+    match pe {
+        Ok((_, (s, e))) => {
+            println!(
+                "ok, span for expression: {:?}, \n\tline: {:?}, \n\tcolumn: {:?}\n",
+                s,
+                s.line,
+                s.get_column()
+            );
+            println!("raw e: {:?}\n", &e);
+            println!("pretty e: {}\n", dump_expr(&(s, e)));
+        }
+        Err(Err::Failure(Error(_, Some(s), err))) => {
+            println!(
+                "{:?} error at:\n\tline: {:?}\n\tcolumn: {:?}\n\tValue: {:?}\n",
+                err,
+                s.line,
+                s.get_column(),
+                s.fragment,
+            );
+            println!("raw s: {:?}", &s);
+        }
+        Err(err) => Err(err).unwrap(),
+    }
+}
+
+// In this example, we have a `parse_expr_ms` is the "top" level parser.
+// It consumes white spaces, allowing the location information to reflect the exact
+// positions in the input file.
+//
+// The dump_expr will create a pretty printing of the expression with spans for
+// each terminal. This will be useful for later for precise type error reporting.
+//
+// The extra field is not used, it can be used for metadata, such as filename.