Predicates
Simple functions that return T or NIL. They have no side effects.
EQ
Tests if to arguments are the same symbol, accepts only symbols or NIL.
>(eq 'pi 'user::pi) T >(eq 'nil ()) ; NIL, 'NIL, () and '() are all EQ T
EQUAL
Tests if two things are the same, is case and type senstive.
>(equal "aa" "AA") NIL >(equal 1 1.0) ; different type NIL
NOT
Logical not. Accepts single argument.
>(not 13) NIL >(not '()) T
ATOM
Tests if the argument is an atom.
>(atom 13) T >(atom nil) ; NIL is an atom (and list) T >(atom '()) ; this is still NIL T >(atom '(a b)) ; this is list NIL
CONSP
Tests if the argument is a cons cell.
>(consp '()) ; NIL is not cons NIL >(consp '(a b)) T
LISTP
Tests if the argument is a list, that means cons-cell or nil.
>(listp nil) ; NIL is a list (and atom) T >(listp '(a b)) T >(listp (cons 'a 'b)) ; this is conscell with B in cdr, improper list T
PROPER-LIST-P
Tests if the argument is a proper list. Proper list means list ending with NIL in the cdr of the last cons cell. Improper list might be dotted, or even cyclic.
>(proper-list-p (cons 'a 'b)) ; this is conscell with B in cdr, improper list NIL
SYMBOLP
Tests if the argument is a symbol. All versions of NIL are symbol.
>(symbolp 'a) ; symbol A T >(symbolp 13) NIL >(symbolp nil) ; symbol NIL T
STRINGP
Tests if the argument is a string.
>(stringp "hello") T >(stringp 'hello) NIL
NUMBERP
Tests if the argument is a number (integer or float).
>(numberp pi) T >(numberp (/ 10 5)) T >(numberp (/ 10 0)) ;Division by zero. NIL
INTEGERP
Tests if the argument is a integer number.
>(integerp (/ 10 5)) ; integer division T >(integerp (/ 10 5.0)) ; poisoned by float 5.0 NIL
ZEROP
Tests if the argument is number zero.
>(zerop (- 10 10)) T >(zerop nil) ;Applying ZEROP on non-numeric data type! NIL
ODDP
Tests if the argument is an odd integer.
>(oddp 3) T >(oddp 3.0) ;Applying ODDP on non-integral number! NIL
EVENP
Tests if the argument is an even integer.
>(evenp 2) T >(evenp 0) T
FUNCTIONP
Tests if the argument is a function object.
>(functionp #'+) T
PACKAGEP
Tests if the argument is a package object.
>(packagep *package*) T
BOUNDP
Expects symbol as argument. Tests if the symbol has value binding.
>(boundp 'pi) T
FBOUNDP
Expects symbol as argument. Tests if the symbol has function or macro binding.
>(fboundp '+) T >(fboundp 'if) ; also works for special forms T
SPECIAL-OPERATOR-P
Expects symbol as argument. Tests if the symbol represents special operator.
>(special-operator-p '+) ; ordinary function NIL >(special-operator-p 'if) ; special operator IF T