is (leftValue rightValue -- isIdentityLike)

Builtins

Name introduction, declaration modifiers, and module binding: NAME: ...;, codeRef, def, exportFunction, importFunction, importVariable, overload, private, static, use, and virtual.
Struct construction forms: (...), {...}, and array.
Selection forms: source-text selection with NAME and .NAME, read-only source-text selection with @NAME and .@NAME, and ordinal or known-name data-input selection with @, callField, and fieldRead.
Writing forms: source-text selection with !NAME and .!NAME, ordinal selection with ! and fieldWrite, and already-selected destination replacement with set.
Calling and control flow: call, if, loop, ucall, and uif.
Text operations: &, LF, attribute, textSize, and textSplit.
Condition constants, value comparison, and logical operators: <, =, >, DEBUG, FALSE, TRUE, and, is, lshift, or, rshift, xor, and ~.
Arithmetic and numeric transforms: *, +, -, /, ^, cast, ceil, cos, floor, log, log10, mod, neg, sin, and sqrt.
Reference, creation, and value-state operations: const, dynamic, isConst, isDirty, isDynamic, isRef, isStatic, known?, new, newVarOfTheSameType, stable?, unconst, and unknownStable?.
Schema and struct introspection: code?, codeRef?, fieldCount, fieldIndex, fieldIsRef, fieldIsVirtual, fieldName, has, isCombined, managed?, same, schemaName, and virtual?.
Storage and manual lifetime operations: addressToReference, alignment, manuallyDestroyVariable, manuallyInitVariable, storageAddress, and storageSize.
Diagnostics and compile-time failure: failCompilation, getCallTrace, printCompilerMessage, printStack, printStackTrace, and raiseStaticError.

is (leftValue rightValue -- isIdentityLike)

Inputs

leftValue: First compared value.

rightValue: Second compared value.

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 compares dereferenced values by identity-like equality.

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

is answers a different question from = and same. Use = for dereferenced value equality 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 values, the builtin returns FALSE even when same and = would both return TRUE.

For Ref values, known Ref values compare by target identity, so two Ref values to different equal-valued targets still give FALSE.

For Text, known Text values compare by their contents.

For Code, two known NIL values give TRUE. Known non-NIL Code values give FALSE. Unknown Code values produce an unknown Cond result.

If supported values are unknown, 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 first: 7; second: 7; textA: 0 ("") dynamic @; 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