Module path mapping.

empty is an empty module path mapping.

Exception raised if an attempt is made to map an already mapped module (including the root).

set_root dir m sets the library root of m to be dir.

• raises Already_mapped

  if library root of m is already set.

add mp fp map extends the mapping map by associating the module path mp to the file path fp.

• raises Already_mapped

  when mp isalready mapped in m.

Exception raised if an attempt is made to use the get function prior to the root being set (using set_root).

get mp map obtains the filename corresponding to the module path mp in map (with no particular extension).

• raises Root_not_set

  when the root of map has not been set using set_root.

iter f map calls function f on every binding stored in map.

pp ppf t prints t on formatter ppf (for debug).