Various Small Fires and Code

Tuesday, November 22, 2016

Payasan notes - Concatenation vs. Extension

Classically constructive combinator libraries favour concatenation [1] - pretty printing is the obvious example: composition operators are functions Doc -> Doc -> Doc or their many-to-one, list equivalents [Doc] -> Doc. The Monoid typeclass is a fundamental part of Glasgow Haskell's standard libraries. When things don't fit Monoid, a standard exception is that they have more than one "plus" operation; pretty printing has two obvious versions of plus - vertical and horizontal concatenation.

However concatenation is not always the the most natural way to construct things. Sometimes extension feels more appropriate. Andy Gill's Graphiz/Dot and Oleg Kiselyov's SXML combinator libraries are compelling examples. In Dot, graphs are built in a monad which enables binding of fresh node ids and the subsequent use of these ids to construct edges. XML pages follow a tree structure - adding and extending leaves is natural whereas concatenating them is unusual and would demand a novel API.

[1] "Constructive" here means combinator libraries that construct something, e.g. a Doc in pretty printing or music (MIDI) in vintage Haskore. This is a loose term and can include, for example parser combinators. Whilst parser combinators process input, a user still builds a parser by concatenating smaller ones together.

Wednesday, November 9, 2016

payasan notes

Clocktime representation - a representation where timing (duration, onset) is represented by some real number and could support some notion of e.g. scaling.

The clock may commonly be seconds but it could be e.g. MIDI ticks.

Metrical representation - a representation where timing (duration) is represented by a symbolic value denoting a metric unit (e.g a quarter note) possibly dotted.

A metrical representation, like staff notation, can be thought of as tiled - no gaps (rests are concrete objects within the representation), no overlaps. Onset is implicit due to tiling. A metrical representation is expected to easily support concatenation.

Thursday, October 15, 2015


I've been working steadily on Payasan and I've now got chord note and fret diagram output working for fret diagrams.

As GitHub counts successive commits and helpfully tells you how long your current streak is I haven't felt the need to blog here about each commit. Also while I'm happy with the progress of Payasan, I think it is going to be a highly idiomatic system (i.e. it will make sense for me, but it will be too "special case" for other users) so publicly blogging about it is not a priority.

Friday, September 18, 2015


I've implemented "chordmode" for Payasan patterned after LilyPond's chordmode.

Chordmode is intended as an intermediate layer for working with chords - LilyPond's chordmode is a bit inscrutable at some points and I believe I have a simpler representation for building and manipulating chords.

The implementation points to quite a few horrors in the module organization of Payasan that I will need to address. I already have 70 modules in the src directory which is excessive and I'll have to do something about combining some of them.

Monday, September 14, 2015


Most of the work is now in place for LilyPond percussion notelists. Some work on rendering is still outstanding.

Sunday, September 13, 2015


I've started to add support for LilyPond drum pitches. This work should point out what bits of Payasan need parameterizing on Pitch. The syntax is already polymorphic on pitch and duration, but so far I haven't treated the parsers and renderers systematically.

Friday, September 11, 2015


I've implemented "full score" output for ABC and LilyPond rather than just output of note list fragments.

It is an expectation of Payasan that the output will be hand-edited after generation if the user wants to create proper scores. However, to "debug" note lists after they have been built, transformed, etc. a user needs to generate a "full score" that can be automatically rendered by LilyPond or ABC to see their work.

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Disambiguating biog as there are a few Stephen Tetley's in the world. I'm neither a cage fighter or yachtsman. I studied Fine Art in the nineties (foundation Bradford 1992, degree Cheltenham 1992 - 95) then Computing part-time at Leeds Met graduating in 2003. I'm the Stephen Tetley on Haskell Cafe and Stackoverflow.