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::>());
let v = mkvec!((0..10).map(|x| x * 2));
defmac!(repeat ref s, n => (0..n).map(|_| &s[..]).collect::());
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]);
}
```