This is a package originally made by Greg Nelson, to make it easy to pretty print parse trees. The documentation is in the interface.

Some of my extensions were made after the point at which interface stability became desirable. I thus created UnparserBufferExtras. Unlike many Extras interfaces, this one contains the union of the base interface and the new stuff rather than the difference; this is so that a client program is less cluttered by the fact that an Extras interface exists.

UnparserBufferExtras provides formatted output routines. Send a stream of characters through a buffer, delineate the stream into subsequences called objects. The objects can be nested. (Objects are called "groups" in CGN9.) For each object, specify within it a set of breakpoints. The routines will format the text as follows. (1) An object will be printed all on one line if possible. (2) If an object cannot fit on one line, new lines will be started at one or more of the object's breakpoints, so that no text overflows the right margin. (3) With each breakpoint there is associated an integer call the breakpoint's offset. If a new line is started at a breakpoint, then the new line will be indented by the sum of the breakpoint's offset plus the indentation of the first character of the smallest object that contains the breakpoint. (4) Each breakpoint is labelled with the rules used for determining if it breaks. There are six sets of rules available: (width) break if and only if necessary to avoid overflowing the right margin; (united) like width, but also break if the smallest containing object contains (recursively) a breakpoint that breaks; (left-looking) like width, but also break if an object between the breakpoint in question and the preceeding breakpoint directly in the smallest enclosing object, if any, else the beginning of the smallest enclosing object, breaks; (always) always break; (miser) break only if necessary after trying all other breakpoints; and (never) never breaks (5) Each breakpoint has a sep, which is a string. If that breakpoint does not break, that string is inserted into the text after the breakpoint. If the breakpoint does break, the string is not inserted into the text.

StructuredStreams provides an IO.STREAM style interface to UnparserBuffer. Again, documented in the interface.