1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
# Idioms
_This document describes common idioms when using Metalang99, i.e., code patterns that have not been reified into abstractions yet._
## Detecting a keyword followed by parentheses
To detect something like `abracadabra(1, 2, 3)`, follow this simple pattern:
```c
#define DETECT_ABRACADABRA(x) ML99_IS_TUPLE(ML99_CAT(DETECT_ABRACADABRA_, x))
#define DETECT_ABRACADABRA_abracadabra(...) ()
// 1
DETECT_ABRACADABRA(abracadabra(1, 2, 3))
// 0
DETECT_ABRACADABRA(blah)
```
## Extracting a value of a keyword followed by parentheses
To get `1, 2, 3` from `abracadabra(1, 2, 3)`:
```c
#define EXTRACT_ABRACADABRA(x) ML99_CAT(EXTRACT_ABRACADABRA_, x)
#define EXTRACT_ABRACADABRA_abracadabra(...) __VA_ARGS__
// 1, 2, 3
EXTRACT_ABRACADABRA(abracadabra(1, 2, 3))
```
## Interspersing a comma
To intersperse a comma between one or more elements, put a comma before each element and pass them all to `ML99_variadicsTail`:
```c
#define ARRAY_SUBSCRIPTS(array, n) \
ML99_EVAL(ML99_variadicsTail(ML99_repeat(v(n), ML99_appl(v(GEN_SUBSCRIPT), v(array)))))
#define GEN_SUBSCRIPT_IMPL(array, i) v(, (array)[i])
#define GEN_SUBSCRIPT_ARITY 2
// (animals)[0], (animals)[1], (animals)[2]
ARRAY_SUBSCRIPTS(animals, 3)
```
|
