86 lines
2.2 KiB
Text
86 lines
2.2 KiB
Text
|
(* 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
|