Confold

The `<:` prefix operator, which marks an expression as a compile-time constant.

    use Confold;

    my $x = <: 42;         # folded at compile time
    my $y = <: "hello";    # folded at compile time
    my $z = <: $variable;  # runtime: creates immutable copy

When the operand is a literal, the operator is folded away entirely and leaves
a plain constant behind, with no runtime overhead at all. When it is not, a
runtime path produces an immutable copy of the value.

The operator says something to the compiler that a function call cannot. Once
an expression is wrapped in an `entersub`, every call checker and optimisation
pass downstream has lost sight of what it contains; `<:` is visible earlier, so
a value marked with it can still be recognised as simple.

The immutable copy is the same promise enforced at run time. Perl aliases `@_`
to the caller's variables, so an ordinary argument can be modified by the sub
it is passed to. An argument marked with `<:` cannot.

`<:` binds as tightly as `\` and unary minus, so it takes the smallest term to
its right: `<: $a + $b` means `(<: $a) + $b`. It is lexically scoped, and it is
recognised while tokenising code only, so quoted text, here-documents and
regular expressions are never affected.


REQUIREMENTS

Requires perl 5.38 or newer, for the core PL_infix_plugin hook the operator is
built on. The operator is the module's only purpose, so it does not install on
older perls. No other dependencies.


INSTALLATION

    perl Makefile.PL
    make
    make test
    make install


SUPPORT AND DOCUMENTATION

    perldoc Confold


LICENSE AND COPYRIGHT

This software is Copyright (c) 2026 by LNATION <email@lnation.org>.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)