verify-car-cdr-switch

As with all compiler switch variables, the value of this variable can be t, nil, or a function object that accepts five arguments and returns t or nil. The arguments passed to the function will be the values of the safety, space, speed, debug, and compilation-speed optimization qualities, in that order. nil is equivalent to a function that always returns nil and t to a function that always returns t. When the value is a function and we say t (or true) or nil (or false) in the text below, we mean that the function returns, respectively, t or nil.

If true, code calling car and cdr will check that the argument is appropriate (i.e. a list). The switch is only effective on platforms which have :verify-car-cdr on the *features* list. Platforms lacking that feature ignore this switch since the verification is done differently but always. Initially true if speed is less than 3 or safety is greater than 1.

See compiling.htm for information on the compiler.

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This page has had significant revisions compared to the 8.1 page.
Created 2016.6.21.