PCALL : UTILITYPCALL is an utility.
(PCALL operation arg1 ... argn)
is used inside functions whose output depends on the current value of
the STYLE parameter. operation is typically something like PRINT-TYPESYM,
or BEGIN-ENVIRONMENT. It expands in such a way that all the styles known
at compile-time are compiled in-line, but it will also work for styles
defined later, e.g. when another package is loaded. arg1 ... argn are
handed to the function which is supposed to perform operation in the
current style. If an operation has not been defined for a particular
style, a THROWFAIL with an appropriate error message will be done.
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