A Perl 6 grandpa operator
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README.md

NAME

Operator::grandpa - An object recursion operator

VERSION

0.01

SYNOPSIS

class Node {
  has $.name;
  has $.parent;
}

my $child = Node.new(
  :name("out"),
  :parent( Node.new(
    :name("mid"),
    :parent( Node.new(
      :name("inner"),
      :parent( Node.new( :name("root") ) )
    ))
  ))
);

my $root1 = $child :| { .parent }
my $root2 = $child 𝄇 -> $node { $node.parent }

DESCRIPTION

multi sub prefix:<:|>(Any --> Callable:D)
multi sub prefix:<𝄇>(Any --> Callable:D)

The grandpa / object recursion operator :| and it's unicode counterpart 𝄇 (U+1D107) invoke the callable on the RHS recursively.

The callable gets initially invoked with the LHS as the argument, and then recursively invoked with its' respective previous return value as the argument.

It does that until the code block evaluates to Any, then returns the last good value.

Note, that if you assign to $_ within the code block, this also changes the LHS of the operator. So, don't do that, unless that's what you want.

multi sub prefix:<|:>(Any --> Callable:D)
multi sub prefix:<𝄆>(Any --> Callable:D)

Alternatively you can use this version of the operator, which does the same as above but operates on a copy of the LHS, thus allowing assigning to $_ safely.

AUTHOR

holli.holzer@gmail.com

COPYRIGHT AND LICENSE

Copyright © holli.holzer@gmail.com

License: Artistic-2.0

This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.