Re: memory costs of storing lambdas?

[Mikael Djurfeldt <djurfeldt@nada.kth.se>]

Han-Wen Nienhuys <hanwen@cs.uu.nl> writes:

> 1. using anon functions:
>
>   (define (style-setter style)
>     (lambda (head) (set-note-head-style head style)))
>   ...
>
>   \property Voice.NoteHead \set #'style-procedure
>     = #(style-setter "cross")
>
> During the lilypond run, the anonymous function is called. Storage
> cost: one anonymous function

According to eval.c:scm_closure and procs.h:

closure = < closcar, env >
closcar = < code, properties >
code = < formals, body >

So, the extra cost (not counting the cost of the list of expressions
in `body') is 3 pairs + pairs in formals list.

In your case, you also surround the closure with an environment
captured by the closure.  This environment has the structure
(explained in the Guile docs):

new-env = < frame, env >
frame = < formals, values >
formals = < 'style, '() >
values = < style-value, '() >

So, you have 4 pairs for the environment, 3 pairs for closure
overhead, 1 pair for formals list, 1 pair for list of expressions in
body, and, 3 pairs for the expression.  So, in total, the object
returned by `style-setter' above will consume 12 pairs.

> During the lilypond-run, a note-head pointer is prepended to the
> argument list, and the list (set-note-head-style head style) is
> evaluated.
>
> Storage cost: a list of length 2.

If you have only two items to store, the most efficient data structure
available is one pair.

For more items, the most efficient structure is a GOOPS object or a
vector.  The cost of ordinary (not applicable) GOOPS objects is one
pair + mallocated memory of size sizeof(ptr) * n where n is number of
items.

Best regards,
Mikael


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