Where can I find reasonable definitions of ''Identity predicates'(?) that we use in our own .scm files?

[James]

Hello,

As part of a tracker issue and for my own education I'm trying to
understand the 'types' (if that is the correct term - from Wikipedia
of Scheme I'm wondering of they are 'Identity predicates') of the
variables (again if that is the correct term) in the listings in some
of the scm files.

For example in the printed IR I might see:

--snip--
figuredBassAlterationDirection (direction)
Where to put alterations relative to the main figure.

figuredBassFormatter (procedure)
A routine generating a markup for a bass figure.

ignoreFiguredBassRest (boolean)
Don’t swallow rest events.

implicitBassFigures (list)
A list of bass figures that are not printed as numbers, but only as
--snip--

What I am interested in are the different 'types' ((list), (boolean),
(procedure), (direction) and so on) and what they mean in a scm
context so I can assign correct text strings for documentation. So if
I had a Property of ABC and I wanted to use a True or False or maybe a
single integer and so on, which would be the correct 'type' to list.

I'm not asking for specific answers in as much as pointer to a scm
website perhaps or some online doc that I could look at and glean.

I'm trying to create a new scm/paper-properties.scm type-file to help
move forward 'http://code.google.com/p/lilypond/issues/detail?id=1392',
I am well out of my comfort/knowledge zone I realise, but am hoping to
get an idea of how the whole autogenerated doc process for things like
Appendixes and the IR work by 'having a go'.

-- 
--

James