Rewrites a file's layout without altering its token sequence.

Backs mix tptp.format. The guarantee is stronger than the canonical printer's: the tokens are unchanged — not the same structure, but the same tokens, in the same order, with the same spellings. Only the white space between them differs.

iex> Tptp.Printer.Format.to_string("fof( a,axiom,p&q ).  % why\n")
"fof(a, axiom, p & q).  % why\n"

Relation to the canonical printer

Tptp.Printer.Canonical reconstructs output from the tree, so anything the grammar admits in more than one form is emitted in the canonical one. That is correct for a canonical form and incorrect for a formatter, which must not alter a file it was asked to lay out. This module therefore operates on the tokens, which are what the source contained.

Comment placement

Reattaching comments is ordinarily the difficult part of a format-preserving printer. Here comments and statements are already ordered by position, so merging the two sequences and examining the white space preceding each item determines the placement:

• no newline before a comment indicates that something preceded it on its line, so it is a trailing comment and remains one;
• one newline places it on its own line;
• two or more preserve the blank line above it, since paragraphing carries information.

This requires a single pass and no position-keyed map.

Unparseable input

A source containing a lexical error is returned unchanged. A formatter is invoked precisely when a file is in an inconsistent state, and rewriting one whose tokens are not trustworthy risks discarding content.