scan-rulesThis crate provides some macros for quickly parsing values out of text. Roughly speaking, it does the inverse of the print!/format! macros; or, in other words, a similar job to scanf from C.
The macros of interest are:
readln! - reads and scans a line from standard input.try_readln! - like readln!, except it returns a Result instead of panicking.scan! - scans the provided string.If you are interested in implementing support for your own types, see the ScanFromStr trait.
The available abstract scanners can be found in the scanner module.
Links
Here is a simple CLI program that asks the user their name and age. You can run this using cargo run --example ask_age.
```rust
use scan_rules::scanner::Word;
fn main() {
print!("What's your name? ");
let name: String = readln! { (let name: Word
print!("Hi, {}. How old are you? ", name);
readln! {
(let age) => {
// ^~~~~~^ implicitly typed variable binding
let age: i32 = age;
println!("{} years old, huh? Neat.", age);
},
(..other) => println!("`{}` doesn't *look* like a number...", other),
// ^~~~~~^ bind to any input "left over"
}
} ```
This example shows how to parse one of several different syntaxes. You can run this using cargo run --example scan_data.
```rust
use std::collections::BTreeSet;
// Word is an "abstract" scanner; rather than scanning itself, it scans some
// other type using custom rules. In this case, it scans a word into a
// string slice. You can use Word<String> to get an owned string.
use scan_rules::scanner::Word;
enum Data {
Vector(i32, i32, i32),
Truthy(bool),
Words(Vec
fn main() { print!("Enter some data: "); let data = readln! { ("<", let x, ",", let y, ",", let z, ">") => Data::Vector(x, y, z), // ^ pattern terms are comma-separated // ^~^ literal text match
// Rules are tried top-to-bottom, stopping as soon as one matches.
(let b) => Data::Truthy(b),
("yes") => Data::Truthy(true),
("no") => Data::Truthy(false),
("words:", [ let words: Word<String> ],+) => Data::Words(words),
// ^~~~~~~~~~~~~~~~~~~~~~~~~~~~^ repetition pattern
// ^ one or more matches
// ^ matches must be comma-separated
("lucky numbers:", [ let ns: i32 ]*: BTreeSet<_>) => Data::Lucky(ns),
// collect into specific type ^~~~~~~~~~~~^
// ^ zero or more (you might be unlucky!)
// (no separator this time)
// Rather than scanning a sequence of values and collecting them into
// a `BTreeSet`, we can instead scan the `BTreeSet` *directly*. This
// scans the syntax `BTreeSet` uses when printed using `{:?}`:
// `{1, 5, 13, ...}`.
("lucky numbers:", let ns) => Data::Lucky(ns),
(..other) => Data::Other(String::from(other))
};
println!("data: {:?}", data);
} ```
This example demonstrates using runtime scanners and the let_scan! convenience macro. You can run this using cargo run --example runtime_scanners.
```rust
use scanrules::scanner::{ NonSpace, Number, Word, // static scanners maxwidtha, exactwidtha, restr, // runtime scanners };
fn main() { // Adapted example from http://en.cppreference.com/w/cpp/io/c/fscanf. let inp = "25 54.32E-1 Thompson 56789 0123 56ß水";
// `let_scan!` avoids the need for indentation and braces, but only supports
// a single pattern, and panics if anything goes wrong.
let_scan!(inp; (
let i: i32, let x: f32, let str1 <| max_width_a::<NonSpace>(9),
// use runtime scanner ^~~~~~~~~~~~~~~~~~~~~~~~~~~~^
// limit maximum width of a... ^~~~~~~~~~^
// ...static NonSpace scanner... ^~~~~~~^
// 9 bytes ^
let j <| exact_width_a::<i32>(2), let y: f32, let _: Number,
// ^~~~~~~~~~~~~~~~~~~~~~~~~^ scan an i32 with exactly 2 digits
let str2 <| re_str(r"^[0-9]{1,3}"), let warr: Word
// ^~~~~~~~~~~~~~~~~~~~~~~~^ scan using a regular expression
));
println!(
"Converted fields:\n\
i = {i:?}\n\
x = {x:?}\n\
str1 = {str1:?}\n\
j = {j:?}\n\
y = {y:?}\n\
str2 = {str2:?}\n\
warr = {warr:?}",
i=i, j=j, x=x, y=y,
str1=str1, str2=str2, warr=warr);
} ```
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