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.

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.