Hi, I am having some trouble understanding the predicates and would really appreciate some explanation.
/* Predicates */ #define isNil(x) ((x)==Nil) #define isTxt(x) (num(x)&1) #define isNum(x) (num(x)&2) #define isSym(x) (num(x)&WORD) #define isSymb(x) ((num(x)&(WORD+2))==WORD) #define isCell(x) (!(num(x)&(2*WORD-1))) I can understand isTxt and isNum - bit 1 set means it's text and bit 2 set means its number. However, why is WORD used for isSym? Could it not have been just 4 and why is does it have to be sizeof(long) - which is also 4 on 32bit but I cant follow the logic. Similarly, isSymb and isCell are confusing to me. Regards, Kashyap
