Hello Aaron, This makes sense. I'll need to be more watchful of mixing Scheme and LilyPond syntax. That's why I couldn't find anything about dot notation the guile manual!
Thank you for the snippet. That is helpful should I need to nest any deeper. Many thanks, mattfong On Sun, Oct 18, 2020 at 10:13 PM Aaron Hill <lilyp...@hillvisions.com> wrote: > On 2020-10-18 5:36 pm, Matthew Fong wrote: > > Hello everyone, > > > > I am likely in over my head with nesting pairs. I read the > > documentation > > link from Jean, and I don't completely understand the internal > > representation of this nesting in scheme. > > > > dictHymn.HymnOne.ID = "210" > > dictHymn.HymnOne.Meter = "8.8.8.8" > > dictHymn.HymnTwo.ID = "344" > > dictHymn.HymnTwo.Meter = "12.12.12.8" > > > > Would it be something like: > > ( ( HymnOne . (( ID . 210 ) ( Meter . "8.8.8.8" )) ) > > ( HymnTwo . (( ID . 344 ) ( Meter . "12.12.12.8" )) ) ) > > Yes, it ends up being an alist of alists. > > > > assoc-get doesn't seem to work here with the syntactic sugar, likely > > because I may not understand how nested pairs work. > > dictHymnValue = #(ly:assoc-get 'ID dictHymn.HymnOne "error") > > \markup \dictHymnValue > > The dot notation I showed is part of LilyPond syntax, not Scheme. > > ly:assoc-get does not support nested alists directly, so you need to > explicitly perform multiple lookups: > > (NOTE: lily-library.scm defines an alias for ly:assoc-get omitting the > ly: prefix.) > > %%%% > \markup #(assoc-get 'ID (assoc-get 'HymnOne dictHymn '()) "error") > \markup #(assoc-get 'Tune (assoc-get 'HymnTwo dictHymn '()) "error") > \markup #(assoc-get 'Meter (assoc-get 'HymnThree dictHymn '()) "error") > %%%% > > If you end up nesting alists more deeply, it can be cumbersome to do all > of the individual assoc-get calls. Here's a recursive wrapper that > accepts a list of keys to lookup one after the other: > > %%%% > #(define (assoc-get* key alist . args) > (if (and (list? key) (not (null? (cdr key)))) > (apply assoc-get* (cdr key) (assoc-get (car key) alist '()) args) > (apply assoc-get (if (pair? key) (car key) key) alist args))) > > foo.one.two.three.four = "!" > \markup #(assoc-get* '(one two three four) foo "?") > \markup #(assoc-get* '(one two five six seven) foo "?") > %%%% > > > -- Aaron Hill >
