Preprocess

Like preprocess in C, Melang supports simple preprocess.

macro

#define NAME 'John' //define macro
#NAME //use macro
#undef NAME //undefine macro

Name is equivalent to ‘John’. Melang just simply replace ‘NAME’ with ‘John’ in code.

condition

//example A
#if NAME
... //code A
#endif

//example B
#if NAME
... //code B
#else
... //code C
#endif

In example A, if NAME is defined, code A will be executed.

In example B, if NAME is defined, code B will be executed, otherwise execute code C.

include

Just like include in C, Melang also support it to load some script files into a file.

Note: the included file must be quoted by double quotes.

e.g.

#include "~/lib.mln"

The path should follow these rules:

• if path is an absolute path, just try to load it.

• if path is not a absolute path, interpreter will search for file in the following order:

  1. if there is the file in current directory, just load it.
  2. if there is a environment variable named MELANG_PATH which points to some directories, interpreter will search for file in them. If interpreter cannot find file, an error would be occurred.
  3. if step 1 and step 2 are failed, interpreter will search for file in /usr/lib/melang/.

  If failed, an error would be occurred.

Another example:

//in /xxx/yyy/a.m

#include "@/b.m"

@ is a special char stands for base directory of current file (a.m). So its value is `/xxx/yyy’.

So /xxx/yyy/b.m will be included in a.m.