prettyprint

A New (2023) SML/NJ Prettyprint library. Version 10.2 (2023.2)

This repository contains implementation files and documentation for new pretty printer library for SML/NJ. This is a two-phase pretty printer where a value to be prettyprinted is first mapped to a format, which is then rendered to printed text (or, potentially, to some "layout" type, such as string).

This new prettyprinter is intended to be installed in smlnj-lib as an alternative to the earlier PP prettyprint library, which is derived from the OCaml Format package.

Features

• flat, static measure of formats

• memoized block measures

• basic and aligned blocks as compound formats

• FLAT format constructor, a format modifier that causes a format to be rendered without line breaks.

• indented formats, another format modifier. Indentation affects the complete content of a format. Indentation is conditional: it is activated for an indented format if and only if the format begins on a fresh line (immediately following that line's indentation).

• styles (format modifier). Generic styles are just strings, which have to be interpreted to impose styles for a given output target. Output targets supporting styles are ANSI terminals and rendering to HTML 3 (smlnj-lib/HTML).

Files

The PrettyPrint library is found in the prettyprint/src directory:

• src/format.sml, the datatypes defining formats

• src/measure.{sig,sml}, computing the static, flat measure of a format

• src/render.{sig,sml}, rendering a format to printed characters

• src/formatting.{sig,sml}, the interface used for writing formatter functions Defines Formatting : FORMATTING

• src/printformats

• src/source.cm, the CM file for compiling the prettyprinter,

• prettyprint-lib.cm, the CM file for compiling the prettyprinter, referring to src/prettyprint.cm.

• CHANGELOG.md, the change log for the new prettyprint library.

Documentation

[The documentation in the two adoc files is currently for Version 8.5, and needs to be updated for Version 10.0 to document styles, for instance.]

The following files are located in the doc directory:

• doc/str-PrettyPrint.{adoc, html}, the interface documentation

• doc/prettyprint-manual.{adoc, html}, the manual for the prettyprinter library

The file MLF2023-talk.pdf contains the slides for MacQueen's talk on the new prettyprint library at the ML Family Workshop, Sept 8, 2023 in Seattle.

A tech report with deeper and broader documentation of the design and its background is being prepared and should be available by the end of September, 2023.