/ 
Syntax-Infix-ConditionalSplice-0.01
/ Syntax::Infix::ConditionalSplice

NAME

Syntax::Infix::ConditionalSplice - a short-circuiting ?| operator for conditional list elements

VERSION

Version 0.01

SYNOPSIS

use Syntax::Infix::ConditionalSplice;

my @cmd = (
    'prog',
    $verbose   ?| '--verbose',          # included only when $verbose
    $jobs > 1  ?| ('--jobs', $jobs),     # a whole sub-list, conditionally
    @files,
);

# equivalent, without the operator:
my @cmd = (
    'prog',
    ($verbose  ? ('--verbose')       : ()),
    ($jobs > 1 ? ('--jobs', $jobs)   : ()),
    @files,
);

DESCRIPTION

Installs a lexically scoped infix operator ?| for conditionally splicing elements into a list. COND ?| LIST evaluates to LIST when COND is true and to the empty list () otherwise -- it is exactly COND ? LIST : (), but reads as one quiet element in the middle of a list instead of a parenthesised ternary with an easily-forgotten : () tail.

Two properties make it more than sugar a function could provide, and are the reason it is built on Infix::Custom's C-level build_op escape hatch:

  • It short-circuits. LIST is only evaluated when COND is true, so $want ?| expensive() never calls expensive() unless $want. A function call cannot do this -- its arguments are all evaluated first.

  • It is context-aware. In list context the true branch flattens its list into the surrounding one; in scalar context COND ?| LIST yields the list's last value (or undef when false), just like the ternary it mirrors.

The entire implementation is one line of C -- a COND_EXPR whose false branch is the empty-list stub:

return newCONDOP(0, lhs, rhs, newOP(OP_STUB, 0));

Precedence

?| binds at assignment precedence: tighter than comma (so $c ?| 'x' is a single list element) but looser than the comparison and logical operators (so the condition can be written without parentheses, e.g. $n > 3 ?| '--big' or $a && $b ?| $x). To make several elements conditional, parenthesise the right-hand side: $c ?| ('a', 'b').

Perl version

Requires perl 5.38 or newer (the PL_infix_plugin hook Infix::Custom builds on); it does not install on older perls.

SEE ALSO

Infix::Custom, Syntax::Infix::OptionalChain

AUTHOR

LNATION <email@lnation.org>

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).