The Comparison Operators , /, <, <=, >, >=

← Prev | ↑ Chapter | Next → | Index | Symbols

The Comparison Operators , /, <, <=, >, >=

The six comparison operators =, /=, <, <=, >, and >= are documented here, next to eq and equal, because they are general comparison predicates: they compare numbers and strings, not numbers only. (Chapter 8, "Numbers", carries a forward-reference to this location.) They differ from eq and equal, which accept arguments of any type: the comparison operators carry a more restrictive argument-type domain — numbers and strings — with a type error on genuinely incompatible non-nil argument types.

Accepted argument-type domain (shared rule)

  • Numbers compare by value across the integer/real tower — e.g. (= 1 1.0) => T — under the coercion rules of "Normative Rules: Number Tower and Division" (chapter 3 / chapter 8).
  • Strings compare by content, and the ordering operators (< <= > >=) order them lexicographically by character code point, left to right. String comparison was verified in BricsCAD V26.
  • Mixed, genuinely incompatible non-nil types — a number against a string, e.g. (< 1 "a") or (= 1 "1") — signal a type error.

  • The nil / bottom (⊥) exception: when any argument is nil, the operator does not signal; it returns nil (⊥ in, ⊥ out). This is the same bottom-propagation rule tracked for the nil distinguished object in chapter 4 (see "Distinguished Object Entry: NIL"). Thus: 

    (< 1 nil)      => nil        ; no error
(< "abc" nil)  => nil        ; no error
(= 1 nil)      => nil        ; no error
(>= nil 1)     => nil        ; no error
(= nil nil)    => nil        ; ⊥ in, ⊥ out (consistent with chapter 4)
(< 1 "a")      -> TYPE ERROR ; two incompatible non-nil types

    The type-error check therefore fires only when all offending arguments are non-nil-but-incompatible; a nil anywhere short-circuits the chain to nil.

  • Variadic chaining holds for strings exactly as for numbers: (< "a" "b" "c") tests each argument against the one to its right, left to right.

See also "Normative Rules: Equality Predicates" (chapter 3), which states these operators alongside eq~/~equal.