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Re: conditional when-property function not working as intended
From: |
David Kastrup |
Subject: |
Re: conditional when-property function not working as intended |
Date: |
Fri, 16 Sep 2016 14:46:50 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux) |
Kieren MacMillan <address@hidden> writes:
> Hi David,
>
> Thank you for the helpful reply and documentation/explanation.
>
>> -- Function: ly:chain-assoc-get key achain default-value
>> strict-checking
>> Return value for KEY from a list of alists ACHAIN. If no entry is
>> found, return DEFAULT-VALUE or â#fâ if DEFAULT-VALUE is not
>> specified. [...]
>>
>> DEFAULT-VALUE is specified as markp, and a markup is never #f. So your
>> condition is always true when the specified KEY cannot be found.
>
> So how could I code the when-property function so that it is false
> when the KEY cannot be found?
By not specifying a default value? I have absolutely no idea why you
put `markp' as the default-value of your call to ly:chain-assoc-get. It
does not serve any purpose conceivable to me, particularly since you are
only planning to use its value when finding the key, and the purpose of
the default-value is to be substituted when _not_ finding the key.
--
David Kastrup
Re: conditional when-property function not working as intended, David Kastrup, 2016/09/15