add equation pretty printer

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
start equation parser implementation

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Fix for-comprehension syntax

This removes several shift/reduce conflicts and is closer to
the spec anyway.

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
fix another reduce/reduce bug

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Fix LR(1) lookahead by mergind token at lex-time

This is somewhat ugly, but works

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>