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P9315   M.G.J. van den Brand
        "Prettyprinting without losing comments"


The problem of prettyprinting in generated programming environments is
addressed. A practical solution for the prettyprinting process itself as
well as for the handling of comments is given.

A new box-language is presented for specifying prettyprint rules in an
algebraic way. Both the syntax and the semantics of this box-language are
formalized. Instead of designing and implementing a formatting machinery in
for example C, the transformation from box-language to (prettyprinted) text
is formally specified. This specification can be executed and its
performance is surprisingly good.

The box-language and its formatting algorithms suggest a general mechanism
to prettyprint text with comments without losing the comments in the
resulting text. There are no restrictions on the form of comments and
places where comments may occur in the text. The method is not based on
adaptions of the abstract syntax tree, but on modifications of the
intermediate box-term that is built when a program is prettyprinted.