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#![no_std] //! A macro to define lambda-like macros inline. //! //! Syntax: //! //! `defmac!(` *name* [ *pattern* [, *pattern* ... ]] `=>` *expression* `)` //! //! *name* is the name of the new macro, followed by 0 or more patterns //! separated by comma. A pattern can be just an argument name like `x` //! or a pattern like `ref value`, `(x, y)` etc. Note that there is no comma //! between the name and the first pattern. //! //! Supports up to four arguments. //! //! # Example //! //! ``` //! #[macro_use] extern crate defmac; //! //! fn main() { //! defmac!(mkvec iter => iter.into_iter().collect::<Vec<_>>()); //! //! let v = mkvec!((0..10).map(|x| x * 2)); //! //! defmac!(repeat ref s, n => (0..n).map(|_| &s[..]).collect::<String>()); //! //! let text = String::from("abc"); //! let s = repeat!(text, 10); //! let t = repeat!("-", s.len()); //! println!("{}", s); //! println!("{}", t); //! //! } //! ``` //! //! Did you know that macros can “capture” variables that they have in scope? //! The capture is by name instead of by reference, so we can use //! defmac where we cannot use closures. See the example below: //! //! ``` //! #[macro_use] extern crate defmac; //! //! fn main() { //! let mut result = Vec::new(); //! let mut sum = 0.; //! let input = "2 2 ^ 7 b ^"; //! //! defmac!(push elem => result.push(elem)); //! defmac!(double => *result.last_mut().unwrap() *= 2); //! //! for ch in input.chars() { //! match ch { //! '^' => double!(), //! '0'...'9' => push!(ch as u32 - '0' as u32), //! 'a'...'z' => push!(ch as u32 - 'a' as u32), //! _ => { } //! } //! } //! //! assert_eq!( //! result, //! vec![2, 4, 7, 2]); //! } //! ``` /// A macro to define lambda-like macros inline. /// /// Syntax: /// /// `defmac!(` *name* [ *pattern* [, *pattern* ... ]] `=>` *expression* `)` /// /// *name* is the name of the new macro, followed by 0 or more patterns /// separated by comma. A pattern can be just an argument name like `x` /// or a pattern like `ref value`, `(x, y)` etc. /// /// Supports up to four arguments. #[macro_export] macro_rules! defmac { ($name:ident => $e:expr) => { macro_rules! $name { () => { $e } } }; ($name:ident $x:pat => $e:expr) => { macro_rules! $name { ($arg:expr) => { match $arg { $x => $e } } } }; ($name:ident $x1:pat, $x2:pat => $e:expr) => { macro_rules! $name { ($a1:expr, $a2:expr) => { match $a1 { $x1 => match $a2 { $x2 => $e } } } } }; ($name:ident $x1:pat, $x2:pat, $x3:pat => $e:expr) => { macro_rules! $name { ($a1:expr, $a2:expr, $a3:expr) => { match $a1 { $x1 => match $a2 { $x2 => match $a3 { $x3 => $e } } } } } }; ($name:ident $x1:pat, $x2:pat, $x3:pat, $x4:pat => $e:expr) => { macro_rules! $name { ($a1:expr, $a2:expr, $a3:expr, $a4:expr) => { match $a1 { $x1 => match $a2 { $x2 => match $a3 { $x3 => match $a4 { $x4 => $e } } } } } } }; } #[cfg(test)] mod tests { #[test] fn it_works() { let value = "xyz"; defmac!(none => value); assert_eq!(none!(), "xyz"); defmac!(one x => x); assert_eq!(one!(2), 2); defmac!(two x, y => x + y); assert_eq!(two!(1., 2.), 3.); defmac!(three x, y, z => (x, y, z)); assert_eq!(three!(1, (2, 3), (4, 5, 6)), (1, (2, 3), (4, 5, 6))); defmac!(four w, x, y, z => (w + x, z, y)); assert_eq!(four!(3, 4, "a", "b"), (7, "b", "a")); } }