Re: apply function incongruity

On 27/06/2018 20:33, Michael Rice wrote:

> Welcome to DrRacket, version 6.7 [3m].
> Language: R5RS; memory limit: 128 MB.
>  > (apply and '(#t #t #f #t))
> . and: bad syntax in: and
>  > (apply + '(1 2 3))
> 6
>  > (and #t #t #f #t)
> #f
>  > (+ 1 2 3)
> 6
> 
> Why do they differ?

+ is a function, and is a macro or syntax transformer, depending on your 
terminological preferences.

apply is a function as well, taking another function (+ in your case) as 
its first argument. You can't pass in and, which in fact corresponds to 
nothing at all at the runtime of your program. The compiler replaces it 
with other code. In your particular case, with all arguments constant, 
the compiler replaces (and #t #t #f #t) by just #f. Using and anywhere 
else than as the first symbol of a list is a syntax error, as you have 
found out experimentally.

Konrad.

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