Re: Universal default value function

[Aaron Hill]

On 2021-01-24 8:17 pm, Vaughan McAlley wrote:
> Hi,
>
> I am trying to write a function that will accept a symbol and a value, 
> and
> assign that value to the symbol *if the variable has not already been
> defined *(such as in an include file).
>
> At the moment, it runs without complaining, but the result is always 
> "bar",
> the default value. Can anyone spot the problem?

Did you mean to attach or include a code snippet?  Hard to spot any 
problem without it.  :)

Regardless, review the following:

%%%%
\version "2.22.0"

valueOrDefault =
#(define-scheme-function
  (module symbol default)
  ((module? (current-module)) symbol? scheme?)
  (module-ref module symbol default))

defineOnce =
#(define-void-function
  (module symbol value)
  ((module? (current-module)) symbol? scheme?)
  (or (module-defined? module symbol)
      (module-define! module symbol value)))

{
  \valueOrDefault foo { b'1 }
  \defineOnce foo { b'4 4 2 }
  \valueOrDefault foo { b'1 }
  \defineOnce foo { b'8 8 2. }
  \foo
}
%%%%

I included the optional module parameter in the event that users might 
need to work outside the current scope.


-- Aaron Hill