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sprint does not accept nil returned from expression

liorscotland

Hello all.
See this behaviour (6.1.6) in SKILL, straight from the CIW (toplevel is 'ils):
It would appear that if the first argument is nil returned from an expression, sprintf won't accept it.
However, "direct" nil works like a charm...
See CIW log below: if( 1== 0 t nil ) ireturns nil, but not accepted as 1st argument to sprint:

sprintf( if( 1==0 t nil ) "yo!\n" )
*Error* sprintf: argument #1 must be a symbol or nil - if((1 == 0) t nil)

if( 1==0 t nil )
nil
sprintf( nil "yo!\n" )
"yo!\n"

Thanks.

  • Hi Lior,

    That's not surprising. sprintf() is a syntax form which doesn't evaluate its first argument - it takes it literally because it's the unquoted name of a variable; if it evaluated it, then you'd have to quote the variable name. If the symbol is nil, then it doesn't assign the value, just returns it. In fact we're making gets() follow a similar model (I suggested this) - recall you asked for a form for gets() which doesn't require a variable.

    Anyway, why would you want to have the first argument be an expression? That seems a bit odd...

    Regards,

    Andrew.

  • Hi Andrew.
    I've it as a part of Macro.
    I need to process the arguments, and I just processed all of them. Instead, I now process the cdr of them
    I do not know what is a syntax form. I need to kook it up.

    -Lior

  • Hi Lior,

    If it's a macro, I'm sure there's no need to do this. Can you share the macro? Maybe if not on the forums, you can send it to me directly?

    A syntax form is something that is built-in to the language - essentially it doesn't evaluate its arguments before it is called (like a normal "lambda" function), but the function can choose which arguments should be evaluated. So language features like procedure, setq, let etc are syntax forms.

    Regards,

    Andrew.

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