examples/main.rs

examples/main.rs

+extern crate nom;
+
+use nom::combinator::map_res;
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{digit1, multispace0},
+    combinator::map,
+    error::{context, VerboseError, VerboseErrorKind},
+    sequence::{preceded, tuple},
+    IResult,
+};
+
+#[derive(Debug, PartialEq)]
+pub enum Op {
+    Add,
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Expr {
+    Num(i32),
+    BinOp(Box<Expr>, Op, Box<Expr>),
+}
+
+pub fn parse_i32(i: &str) -> IResult<&str, Expr> {
+    map(digit1, |digit_str: &str| {
+        Expr::Num(digit_str.parse::<i32>().unwrap())
+    })(i)
+}
+
+fn parse_expr(input: &str) -> IResult<&str, Expr> {
+    preceded(
+        multispace0,
+        alt((
+            map(
+                tuple((parse_i32, preceded(multispace0, tag("+")), parse_expr)),
+                |(l, _, r)| Expr::BinOp(Box::new(l), Op::Add, Box::new(r)),
+            ),
+            parse_i32,
+        )),
+    )(input)
+}
+
+// cargo test
+#[test]
+fn test_parse_i32_1() {
+    let res = parse_expr("2");
+    assert!(res == Ok(("", Expr::Num(1))))
+}
+
+#[test]
+fn test_parse_i32_2() {
+    let _ = parse_expr("1a").is_ok();
+}
+
+fn main() {
+    println!("{:?}", parse_expr("1"));
+    println!("{:?}", parse_expr("1+2 + 3"));
+    println!("{:?}", parse_expr("   1+ 1a"));
+    println!("{:?}", parse_expr("11111111111111111111111111"));
+}