User defined pipe and redirection operators: Difference between revisions
User defined pipe and redirection operators (view source)
Revision as of 01:14, 4 June 2017
, 6 years ago→{{header|Perl 6}}: Add a Perl6 example
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Thundergnat (talk | contribs) (→{{header|Perl 6}}: Add a Perl6 example) |
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print while $_ = $chain->readline;</lang>
=={{header|Perl 6}}==
Implementing cat, redirect(<), head, tail and tee. I share the same general lack of enthusiasm as the Perl example author to implement other the shell ops. Many of the ops already exist in some form in Perl 6, though they may have slightly different syntax and precedence as the shell ops. I didn't bother implementing pipe (|) as Perl 6 pretty much has chaining semantics built in.
The less than '<' operator is pretty low level in Perl 6 and would be troublesome to override, so is implemented as 'redirect'. The sort and unique directives don't really have any effect on the final result string, it would be the same without them, but it is following the task example.
This assumes that the data is in a tab separated file "List_of_computer_scientists.lst" in the current directory.
<lang perl6>sub cat ($fname) { lazy $fname.IO.lines };
sub head ($count, @positional) { @positional.head($count) }
sub redirect ($fname) { cat($fname) }
sub tail (Int $count, Str $fname) { $fname.IO.lines.tail($count) }
sub infix:<tee> ($stream, $fname) {
# need to reify the lazy list to write to a file
my @values = @$stream[^Inf].grep: *.defined;
# meh. not really going to write the files
# $fname.IO.put @values.join("\n")
# just pass the reified values along
@values.List
}
my $aa = ((
(head 4, redirect 'List_of_computer_scientists.lst'),
cat('List_of_computer_scientists.lst') .grep( /'ALGOL'/ ) tee 'ALGOL_pioneers.lst',
tail 4, 'List_of_computer_scientists.lst'
).flat .sort .unique tee 'the_important_scientists.lst') .grep: /'aa'/;
say "Pioneer: $aa";</lang>
{{out}}
<pre>Pioneer: Adriaan van Wijngaarden Dutch pioneer; ARRA, ALGOL</pre>
=={{header|Racket}}==
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