is (leftValue rightValue -- isIdentityLike)

Inputs

• leftValue: First operand.
• rightValue: Second operand.

Outputs

• isIdentityLike: Cond result that is TRUE when the identity-like comparison holds, and unknown when that comparison cannot be decided at compile time.

is requires matching dereferenced schemas, then applies the identity-like rules below. Ref operands are compared by target identity, not by the values stored in their targets.

All same-schema inputs are accepted. Identity-like equality is meaningful for Ref, Text, and Code objects. Other same-schema inputs return FALSE.

is answers a different question from = and same. Use = for equality of values after dereferencing and same for dereferenced schema identity.

Behavior

• The dereferenced schemas of both inputs must match. If they do not, the call is invalid; it does not return FALSE.
• Matching schema is not enough by itself. For In-place objects, the builtin returns FALSE even when same and = would both return TRUE.
• For Ref objects, known Ref objects compare by target identity, so two Ref objects to different equal-valued targets still give FALSE.
• For Text, known Text objects compare by their contents.
• For Code, two known NIL values give TRUE. Known non-NIL Code objects give FALSE. Unknown Code objects produce an unknown Cond result.
• If supported objects have unknown values, the builtin produces an unknown Cond result with a runtime equality check instead of a known TRUE or FALSE.

Example

{} 0 {} [
  nilCode: {} () {} codeRef;
  compiledCode: {} () {} codeRef;
  [] !compiledCode # a non-NIL Code
  first: 7;
  second: 7;
  textA: 0 ("") dynamic @; # an unknown Text
  textB: 0 ("") dynamic @;

  "-- In-place values --" printCompilerMessage
  7 7 same printStack _:;
  7 7 = printStack _:;
  7 7 is printStack _:;

  "-- Ref values compare target identity --" printCompilerMessage
  @first @first is printStack _:;
  @first @second is printStack _:;

  "-- text compares contents --" printCompilerMessage
  "hi" "hi" is printStack _:;
  "hi" "ho" is printStack _:;

  "-- unknown supported values can produce unknown Cond --" printCompilerMessage
  textA textB is printStack _:;

  "-- code --" printCompilerMessage
  @nilCode @nilCode is printStack _:;
  @compiledCode @compiledCode is printStack _:;

  0
] "main" exportFunction

Expected Output During Compilation

-- In-place values --
TRUE
TRUE
FALSE
-- Ref values compare target identity --
TRUE
FALSE
-- text compares contents --
TRUE
FALSE
-- unknown supported values can produce unknown Cond --
Cond
-- code --
TRUE
Cond

See also

• < builtin (leftValue rightValue -- isLess) Tests whether the left dereferenced object is less than the right one for supported same-schema numeric or known Text objects.
• = builtin (leftValue rightValue -- isEqual) Tests equality of values after dereferencing for Cond, numeric, and Text objects of the same schema.
• > builtin (leftValue rightValue -- isGreater) Tests whether the left dereferenced object is greater than the right one for supported same-schema numeric or known Text objects.
• same builtin (leftSchema rightSchema -- isSameSchema) Tests whether two dereferenced schemas are exactly the same; this is schema equality only, not runtime-value equality.