On 2/11/2012 10:55 AM, Laurent wrote:
Hi,
Often I'd like to make a wrapper for a given function that has default
values (possibly with keywords).
So if I want my function to have the same default values for one
particular optional argument, I need to redefine it myself.
For example, suppose there already exists a function foo like this:
(define (foo arg1 [arg2 <some-complicated-default-value>])
....)
And I want to make a wrapper for foo on arg1, but keep foo's arg2
default value:
(define (bar [arg2 <the-same-complicated-default-value>])
(foo 5 arg2))
But I don't feel right when I need to redefine the default argument,
for a few reasons:
- I feel bar should not need to know foo's arg2 default value.
- if arg2 has a complicated default argument, it is "painful" and
error-prone to rewrite it (and if the docs for the default value for
arg2 are simplified, it may be problematic),
- if the specification of foo's arg2 changes, I need to change bar too
(though sometimes bar's arg2 needs not reflect the change, but often
it does),
I would prefer something like:
(define (bar [arg2 (get-default-value foo arg2)])
(foo 5 arg2))
which is transparent w.r.t. foo.
Does this feature exist, or does it even have a name? Or can it be
easily implemented (maybe keywords could help)?
Thanks,
Laurent
I simply use
(define (bar . x)
(apply foo 5 x))
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