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
|
(* This example shows that the definition of FOO that is nested inside
the (multi-line) definition of BAR affects only the body of the
definition of BAR. It does not affect the text that follows a call
to BAR. So, a multi-line macro definition acts as a scope delimiter. *)
#def BAR
#define FOO "definition of FOO inside BAR"
FOO (* expands to "definition of FOO inside BAR" *)
#enddef
#define FOO "definition of FOO at the top level"
FOO (* expands to "definition of FOO at the top level" *)
BAR
FOO (* expands to "definition of FOO at the top level" *)
(* If one wishes to delimit a scope, without actually defining a macro,
one can use #scope ... #endscope. *)
#scope
#define HELLO "first definition of HELLO"
HELLO (* expands to "first definition of HELLO" *)
#endscope
#scope
#define HELLO "second definition of HELLO"
HELLO (* expands to "second definition of HELLO" *)
#endscope
HELLO (* this does not expand *)
(* The effect of #scope ... #endscope can be simulated by writing
#def DUMMY ... #enddef DUMMY #undef DUMMY
but this is a bit unnatural. *)
#def DUMMY
#define HELLO "definition of HELLO inside the scope"
HELLO (* expands to "definition of HELLO inside the scope" *)
#enddef
DUMMY
#undef DUMMY
HELLO (* this does not expand *)
(* Another simple example. *)
#scope
#define HI "I am defined"
let x = HI (* expands to "I am defined" *)
#endscope
#define HI 42
let y = HI (* expands to 42 *)
(* Check that the effect of #undef is also local.
This example relies on the above definition of HI. *)
#scope
#undef HI
let qwd = HI (* HI is not recognized as a macro and expands to itself *)
#endscope
let z = HI (* expands to 42 *)
(* Scopes can be nested. *)
#define LEVEL 0
let x = LEVEL (* expands to 0 *)
#scope
#undef LEVEL
#define LEVEL 1
let y = LEVEL (* expands to 1 *)
#scope
#undef LEVEL
#define LEVEL 2
let z = LEVEL (* expands to 2 *)
#endscope
let _ = LEVEL (* expands to 1 *)
#endscope
let _ = LEVEL (* expands to 0 *)
(* Another example of nesting. *)
#scope
#define HELLO "Hello, "
#scope
#define MAN "man"
let message1 = HELLO ^ MAN
#endscope
(* Here, MAN is no longer defined, but HELLO still is. *)
let message2 = HELLO ^ "world"
#endscope
|