Normative Rules: Equality Predicates

AutoLISP defines the following equality predicates with the semantics observed in BricsCAD V26 / macOS:

• (eq a b) — pointer-level identity for cons cells, distinguishes freshly-allocated objects, but returns T for two textually-identical string literals (the host interns string literals), and T for two textually-identical symbol literals (canonical case-folded name).
• (equal a b) — structural equality over cons cells; numerically compares an integer to a real ((equal 1 1.0) returns T); compares strings by content.
• Truthiness: a value is true iff it is not nil. 0, 0.0, "" are true. nil is the unique false value.

BricsCAD V26 / macOS direct probe section H–J:

• (equal "abc" "abc") = T ; (eq "abc" "abc") = T — string literals are interned.
• (equal 1 1.0) = T — cross-type numeric equality.
• (equal '(1 2) (list 1 2)) = T ; (eq '(1 2) (list 1 2)) = nil — structural vs identity.
• (if 0 'yes 'no) = YES ; (if 0.0 'yes 'no) = YES ; (if "" 'yes 'no) = YES ; (if '() 'yes 'no) = NO.
• (eq nil '()) = T ; (null nil) = T ; (null '()) = T — nil and the empty list are the same object.

• Compare CLHS 14.5.1 — CL's eq is finer-grained (does not intern strings).
• Compare R7RS 6.1 — Scheme distinguishes eqv?, eq?, and equal?.

Phase-6 BricsCAD V26 / macOS semantics probe sections H, I, J.