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@ksaj @lispwizard @amszmidt @screwtape

On the Symbolics system, the type tags were all encoded in the microcode source and recognized in the hardware (ok, really the microcode). The type tag names were constants whose names all began with "DTP-" (for "data type", probably).

There was a type calld DTP-NULL (see below, page 7, though I think that's for the Ivory chip).

It didn't *quite* mean WTF, but almost. :-)

(No, it was not used this way.)

https://bitsavers.org/pdf/symbolics/I_Machine/Lisp-Machine_Data_Types.pdf