I'm going to port Metapost to a different platform. From the the sources I got mp.web , mp.ch , dvitomp.web , and dvitomp.ch .

Using the *.web files together with the supplied change files (*.ch) by WAEVE and TANGLE works. WEAVE and TANGLE without a change file doesn't work; it looks like this is not implemented. But using an a change file containing only a comment line and a line with a single space also doesn't work; WEAVE and TANGLE must be aborted and the log files only contain

\input webma

As a workaround I used dummy change files like the following:
  % dummy change file to keep MikTeX WEAVE / TANGLE happy

  @x
  \def\title{MetaPost}
  @y
  \def\title{MetaPost}
  @z

which showed no problems. So my questions are:
 - why do the programs not accept a change file containing only commens,
 - can WEAVE / TANGLE be modified (in a future MikTeX version) to work without a changefile?

Regards

Ralf