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
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
|
optcomp - optional compilation with cpp-like directives
=======================================================
Optcomp is a syntax extension which handles `#if`, `#else`,
... directives in ocaml source files.
For example, to switch between two pieces of code according to the
ocaml compiler version, one can write:
#if ocaml_version < (3, 10)
let x = 1
#else
let x = 2
#endif
### What the difference between cpp and optcomp ?
Optcomp is more OCaml-friendly than cpp:
* it does not interpret `//`, `/*`, and `*/` as comment delimiters
* it does not complains about missing `'`
* it is easier to integrate in the build process when using other
camlp4 syntax extensions
By the way optcomp does not do macro expansion while cpp does.
### What the difference between pa_macro and optcomp ?
Optcomp does not require code that will be dropped to be valid caml
code. So for example this code will be rejected by
camlp4(<3.13)+pa_macro:
IFDEF HAVE_GADTS THEN
type 'a t =
| Int : int t
| String : string t
ENDIF
But this one will be accepted by camlp4+optcomp:
#if HAVE_GADTS
type 'a t =
| Int : int t
| String : string t
#endif
Installation
------------
To build and install optcomp:
$ ./configure
$ make
$ make install
### Documentation _(optional)_
To build the documentation:
$ make doc
It will then be installed by `make install`.
### Tests _(optionnal)_
To build and execute tests:
$ ./configure --enable-tests
$ make test
Usage
-----
### As a syntax extension
You can use optcomp as a regular syntax extension with camlp4. If you
have ocamlfind installed, you can use:
$ ocamlfind ocamlc -syntax camlp4o -pakcage camlp4,optcomp file.ml
You can also embed `pa_optcomp.ml` in your project sources.
#### As a preprocessor
Optcomp can be used as a preprocessor, for that there is the two
executable optcomp-o and optcomp-r:
* `optcomp-o` is for when directives are written using original syntax
* `optcomp-r` is for when directives are written using revised syntax
To use them:
$ ocamlc -pp optcomp-o <file.ml>
$ ocamlc -pp optcomp-r <file.ml>
The preprocessor version is especially usefull for .mli because it
does not modify the layout of your code, which is important for
ocamldoc.
Hacking
-------
To add support to more expressions, you can modify the eval function
of pa_optcomp.ml. It takes a camlp4 expression ast and must return
something of type value.
|
