lang/boomerang - The NetBSD Packages Collection

Boomerang is a programming language for writing lenses--well-behaved
bidirectional transformations--that operate on ad-hoc, textual data
formats. Every lens program, when read from left to right, describes
a function that maps an input to an output; when read from right
to left, the very same program describes a "backwards" function
that maps a modified output, together with the original input, back
to a modified input.

Lenses have been used to solve problems across a wide range of
areas in computing including: in data converters and synchronizers,
in parsers and pretty printers, in picklers and unpicklers, in
structure editors, in constraint maintainers for user interfaces,
in software model transformations, in schema evolution, in tools
for managing system configuration files, and in databases where
they provide updatable views.