pro January 2018

pro@common-lisp.net

3 participants
2 discussions

Contradiction between the MOP and the standard ?
by Didier Verna 22 Jan '18

22 Jan '18

Hi, In the CLHS page for ENSURE-GENERIC-FUNCTION, there is this paragraph: "If function-name specifies a generic function that has a different value for the :generic-function-class argument and if the new generic function class is compatible[1] with the old, change-class is called to change the class of the generic function; otherwise an error is signaled." In the AMOP however, one can read the following. >From the page on ENSURE-GENERIC-FUNCTION: "The behavior of this function is actually implemented by the generic function ensure-generic-function-using-class. When ensure-generic-function is called, it immediately calls ensure-generic-function-using-class and returns that result as its own." And then from the page on ENSURE-GENERIC-FUNCTION-USING-CLASS: "If the class of the generic-function-or-nil argument is not the same as the class specified by the :generic-function-class argument, an error is signaled." Let alone the fact that this should only apply when there actually is an existing generic function, this seems to be in contradiction with the Common Lisp standard, as it would explicitly forbid changing the class of the generic function, even in a "compatible" way. Comments? Footnotes: [1] BTW, what does "compatible" mean ? -- Resistance is futile. You will be jazzimilated. Lisp, Jazz, Aïkido: http://www.didierverna.info

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One annoyance of ensure-generic-function-using-class
by Didier Verna 02 Jan '18

02 Jan '18

Hello, there is something annoying with ensure-generic-function-using-class. The MOP specifies that if the :generic-function-class option is not provided, it defaults to standard-generic-function. While this makes perfect sense when the generic function doesn't already exist, it seems to also apply when it does. As a result, if you want to call ensure-generic-function on an existing generic function using a different meta-class, for instance like this: (ensure-generic-function gf-name :generic-function-class (class-of gf)) This is a bit annoying, and I don't understand the rationale behind this, if there's one. Why not defaulting to the existing generic function's meta-class? -- Resistance is futile. You will be jazzimilated. Lisp, Jazz, Aïkido: http://www.didierverna.info

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pro January 2018