Initial commit

.gitignore

+/target
+**/*.rs.bk

.vscode/tasks.json

+{
+    // See https://go.microsoft.com/fwlink/?LinkId=733558 
+    // for the documentation about the tasks.json format
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "type": "cargo",
+            "subcommand": "build",
+            "problemMatcher": [
+                "$rustc"
+            ]
+        }
+    ]
+}
\ No newline at end of file

Cargo.lock

+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
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+
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Cargo.toml

+[package]
+name = "first"
+version = "0.1.0"
+authors = ["Per Lindgren <per.lindgren@ltu.se>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "5.0.1"

src/main.rs

+extern crate nom;
+
+use nom::combinator::map_res;
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete::{digit1, multispace0},
+    combinator::map,
+    error::{VerboseError, VerboseErrorKind},
+    map_res,
+    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, VerboseError<&str>> {
+    map_res(digit1, |digit_str: &str| match digit_str.parse::<i32>() {
+        Err(e) => Err(VerboseError {
+            errors: vec![(digit_str, VerboseErrorKind::Context("not a 32-bit integer"))],
+        }),
+        Ok(x) => Ok(Expr::Num(x)),
+    })(i)
+}
+
+fn parse_expr(input: &str) -> IResult<&str, Expr, VerboseError<&str>> {
+    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)
+}
+
+fn main() {
+    println!("{:?}", parse_expr("1"));
+    println!("{:?}", parse_expr("1+1a"));
+    println!("{:?}", parse_expr("11111111111111111111111111"));
+}