write por

[JanMarvin]

Should be fairly easy to implement now that reading works.

• [x] extract pnum function from TDA to print numerics
• [x] put everything together for writing integers, numerics and strings < 255 chars
• [x] add data and var label
• [x] add value labels
• [x] handle missings
• [x] test everything!

[JanMarvin]

For whatever kind of reason only readspss and SPSS/PSPP can read this files correctly. foreign bails on most of them, haven and memisc import incorrect values.