isConst (value -- isConst)

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.

isConst (value -- isConst)

Inputs

value: Current stack value whose immutability is tested.

Outputs

isConst: Known Cond result that is TRUE when the current stack value is immutable.

isConst is the current stack-value immutability predicate. It tests whether the current stack value itself is immutable.

It tests only the current stack view. The result depends on the value on the stack, not on whether the same underlying storage is also reachable through another Ref with different mutability. The view-changing builtins const and unconst can therefore change this result only for Ref inputs. For Code values, isConst depends only on the current stack value being Code, not on whether that Code value is known, unknown, NIL, or non-NIL.

Behavior

Immutable Ref values report TRUE.

Mutable Ref values report FALSE.

Text values report TRUE, regardless of whether their contents are known at compile time.

Code values report TRUE, including known non-NIL, known NIL, and unknown Code values.

In-place values, Block, and Meta values report FALSE.

NAME on an In-place local produces an immutable Ref view, while @NAME produces a mutable Ref view. The two forms can therefore produce different isConst results.

Example

{} 0 {} [ value: 7; codeLocal: {} () {} codeRef; unknownText: 0 ("") dynamic @; [] !codeLocal "-- mutable versus immutable Ref views --" printCompilerMessage @value isConst printStack _:; value isConst printStack _:; @value const isConst printStack _:; value unconst isConst printStack _:; "-- In-place values --" printCompilerMessage 7 isConst printStack _:; 0 dynamic isConst printStack _:; "-- Text and Code are const stack values --" printCompilerMessage "hi" isConst printStack _:; unknownText isConst printStack _:; {} () {} codeRef isConst printStack _:; {} () {} codeRef dynamic isConst printStack _:; @codeLocal isConst printStack _:; "-- Block and meta are not const stack values --" printCompilerMessage [] isConst printStack _:; () isConst printStack _:; 0 ] "main" exportFunction

Expected Output During Compilation

-- mutable versus immutable Ref views -- FALSE TRUE TRUE FALSE -- In-place values -- FALSE FALSE -- Text and Code are const stack values -- TRUE TRUE TRUE TRUE TRUE -- Block and meta are not const stack values -- FALSE FALSE