Re: [Denemo-devel] Transpose applied to Selection

[Richard Shann]

On Mon, 2008-12-01 at 19:09 +0000, Richard Shann wrote:
> I have succeeded in executing the following script to transpose the
> selection by a major third:
> 
> (define Transpose::Interactive #f)
> (define Transpose::Interval "c e")
> (ApplyToSelection "d-TransposeNotes")
> 
> where d-TransposeNotes is broadly Jeremiah's real_transpositionx.scm
> which just transposes the current note if not interactive. It turned
> out
> that there was no provision for scripts to call scripts, so I have
> done
> the plumbing for this and checked it in. It will be a while before I
> can
> check in these scripts, as the ApplyToSelection function needs
> extracting and putting in the init.denemo file (I think). But it
> works. 

I have looked at the task of using a script like transpose with scripts
like ApplyToSelection, and this has prompted some re-think about the
structure of the interface between Scheme and Denemo.
At present scripts can pass a string to a Denemo command; this is so
that the script can supply the responses which a user would give to any
dialog that the command might invoke. This is fine, but I think we
should have a cleaner looking return value: at the moment the commands
return the string, possibly modified, to the script. This is extremely
flexible, of course, but ugly since you have to start agreeing a set of
messages (in English) and over-the-top as all we need is a return
boolean (either it did it, or it didn't). (We *could* return a status,
but I think that we are better leaving that out: for the rare cases
where we want to know more about failure we can implement an additional
query function that does the action and returns a desired type of
information; by contrast, returning a status already implies creating
some shared table of meanings which has to be maintained and documented
and looked up by the script writer.)
So I propose to introduce a DenemoScriptParameter structure that has a
GString *input_string and gboolean return_value, and then in a script we
can test things like

(if (d-GoToMark)
        (action now that the cursor is at the start of the selection)
        (what to do if there is no selection so that goto_mark failed))

Richard