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Best way to call a user defined hook (written in guile) from C when the
Best way to call a user defined hook (written in guile) from C when the hook need plenty parameters
Mon, 5 Jul 2010 10:56:36 +0200
Frequently, our C program computes a set of approximately 50 values that it
to make accessible for a user defined call back so that the user can choose to
print some of these values (if some condition is met for instance).
I first thought to make some C functions accessible that would return the
values (one C getter per value), and have the C scheme procedure call these
C functions for the values it's interested in. But the problem is that it's
a little verbose (both in C and in scheme due to the required parenthesis).
I then though of binding the values to global variables that the user callback
would use but ruled this out because I was afraid this solution would be slow.
Then I wanted to pass the values as regular parameters, but I don't want to
the user to define his function with 50 parameters.
So finally we came up with something like this :
The user enter merely a list of the values he wants (in a "configuration" file)
(define user-fields `(foo bar (+ baz foo) (if (> foo bar) 1 2)))
And then in C we evaluate :
(define (hook-helper %s) (lambda () #\t))
where %s is the long list of parameters (foo bar baz...) that's inserted by the
(define (hook . args) (local-eval (cons print-user-fields user-fields)
(procedure-environment (apply hook-helper args))))
So the user entry is minimal and we can, for each set of values, apply the hook
function to the values (which is I think one of the fastest way to make
a set of named values to scheme).
The downside is : the above scheme line looks like black magic.
Can anyone suggest a better way to do this ?
- Best way to call a user defined hook (written in guile) from C when the hook need plenty parameters,