LISP I Programmer's Manual - Software Preservation Group

In either case, if a machine-language subPoutine.def$nesa function, the association list for the name of the function(see Section 6.2) contains the indicator fSUBRf to indicatethat a subroutine exists. SUBR in turn points to a transferinstruction of the formTXLsubroutine , , nwhere n is the number of arguments of the function.Thus the relevant part of the association list has thestructure,.. SUBR 1-1 .Ia mTXL subroutine , , nThe other way a function can be defined is by means of aLISP S-expression (representing an M-expression), which is tobe interpreted during the running of a LISP program. In thiscase the indicator 'EXPR' is on the association list for thename of the function. EXPR points to the S-expression definingthe function, as follows:L(S-expressiondefining the function)