/ 
Syntax-Feature-With-0.01
/ Syntax::Feature::With

NAME

Syntax::Feature::With - Simulate Pascal's "with" statement in Perl

SYNOPSIS

use Syntax::Feature::With qw(with with_hash);

my %h = ( a => 1, b => 2 );
my ($a, $b);

# Basic usage
with \%h, sub {
    say $a;   # 1
    $b = 99;  # updates %h
};

# Strict mode
with -strict => \%h, sub {
    say $a;   # ok
    say $b;   # ok
    say $c;   # error: undeclared
};

# Debug mode
with -debug => \%h, sub {
    ...
};

# Trace mode (includes debug)
with -trace => \%h, sub {
    ...
};

# Convenience wrapper
with_hash %h => sub {
    say $a;
};

DESCRIPTION

with() provides a simple, predictable way to temporarily alias hash keys into lexical variables inside a coderef. It is implemented using PadWalker and requires no XS, no parser hooks, and no syntax changes.

FEATURES

Read/write aliasing

Lexicals declared in the outer scope become aliases to hash entries:

my ($a);
with \%h, sub { $a = 10 };   # updates $h{a}

Strict mode

with -strict => \%h, sub { ... };

Every valid hash key must have a matching lexical declared in the outer scope. Missing lexicals cause an immediate error.

Debug mode

with -debug => \%h, sub { ... };

Prints a summary of aliasing decisions:

Aliased: $a -> %hash{a}
Ignored: foo-bar (invalid identifier)
Ignored: y (no lexical declared)

Trace mode

with -trace => \%h, sub { ... };

Shows entry/exit and nesting depth:

[with depth=1] entering with()
Aliased: $a -> %hash{a}
[with depth=1] leaving with()

Trace mode implies debug mode.

Nested with() support

Nested calls work naturally:

with \%h1, sub {
    with \%h2, sub {
        ...
    };
};

with_hash wrapper

Syntactic sugar:

with_hash %h => sub { ... };

AUTHOR

Nigel Horne, <njh at nigelhorne.com>

LIMITATIONS

  • Lexicals must be declared in the outer scope.

  • Only hashrefs are supported.

  • Only keys matching /^[A-Za-z_]\w*$/ are eligible.

AUTHOR

Nigel Horne

REPOSITORY

https://github.com/nigelhorne/Syntax-Feature-With

SUPPORT

This module is provided as-is without any warranty.

Please report any bugs or feature requests to bug-syntax-feature-with at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Syntax-Featre-With. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

You can find documentation for this module with the perldoc command.

perldoc Syntax-Feature-With

You can also look for information at:

LICENCE AND COPYRIGHT

Copyright 2026 Nigel Horne.

Usage is subject to licence terms.

The licence terms of this software are as follows:

  • Personal single user, single computer use: GPL2

  • All other users (including Commercial, Charity, Educational, Government) must apply in writing for a licence for use from Nigel Horne at the above e-mail.