Reading files can't be this simple

Reading a file, line-by-line.

How is such a common task, so simple here in Rakuland?

Why is such a common task, so commonly complicated elsewhere?

Who knows?

You will!

Talk tags
raku, lazy, iterator, iterable, for, while, lines, slurp, X::Control, java, dart, perl

Transcript

1. Reading Files Can’t Be This Simple
 The Raku Conference
 
 2021-08-07
2. Reading Files
 Can’t Be This Simple (recorded in front of a live studio audience) 
 http://speakerdeck.com/util
 <bruce.gray@acm.org> <<< >>> >>> <<<
3. This lightning talk was recorded in an actual
 lightning storm.
4. This lightning talk was recorded in an actual
 lightning storm. ( but *this* video is a re-recording )
5. /me
 
 Bruce Gray
 
 'Util'
6. Reading Files Can’t Be This Simple
7. my $path = 'myFile.txt'; for $path.IO.lines { … }
8. my $path = 'myFile.txt'; for $path.IO.lines { … }
9. my $path = 'myFile.txt'; for $path.IO.lines { … }
10. my $path = 'myFile.txt'; for $path.IO.lines { … }
11. I don't see the glaringly obvious similarity... • Iterator: Give me the next thing. • Iterable: Proceed to the adjacent thing.
12. Big file line by line
13. time raku -e ' my $mb = "abc\ndef\nghi\nEND\n" x 2**16; print $mb for ^1024; ' > gigabyte.txt
14. $ head -8 gigabyte.txt abc def ghi END abc def ghi END
15. import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; public class ReadAL { public static void main(String[] args) throws Exception { for ( String s : Files.lines(Paths.get("gigabyte.txt")) ) { if ( s.startsWith("END") ) break; if ( !s.startsWith("a") ) continue; System.out.println(s); } } }
16. import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; public class ReadAL { public static void main(String[] args) throws Exception { for ( String s : Files.lines(Paths.get("gigabyte.txt")) ) { if ( s.startsWith("END") ) break; if ( !s.startsWith("a") ) continue; System.out.println(s); } } }
17. import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; public class ReadAL { public static void main(String[] args) throws Exception { for ( String s : Files.lines(Paths.get("gigabyte.txt")) ) { if ( s.startsWith("END") ) break; if ( !s.startsWith("a") ) continue; System.out.println(s); } } }
18. import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; public class ReadAL { public static void main(String[] args) throws Exception { for ( String s : Files.lines(Paths.get("gigabyte.txt")) ) { if ( s.startsWith("END") ) break; if ( !s.startsWith("a") ) continue; System.out.println(s); } } }
19. import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; public class ReadAL { public static void main(String[] args) throws Exception { for ( String s : Files.lines(Paths.get("gigabyte.txt")) ) { if ( s.startsWith("END") ) break; if ( !s.startsWith("a") ) continue; System.out.println(s); } } }
20. $ java ReadAL.java ReadAL.java:6: error: 
 for-each not applicable to expression type for ( String s : Files.lines(Paths.get("gigabyte.txt")) ) { ^ required: array or java.lang.Iterable found: Stream<String> 1 error error: compilation failed
22. import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; import java.util.stream.Collectors; public class ReadAL { public static void main(String[] args) throws Exception { Stream<String> fStream = Files.lines(Paths.get("./gigabyte.txt")); for ( String s : fStream.collect( Collectors.toList() ) ) { if ( s.startsWith("END") ) break; if ( !s.startsWith("a") ) continue; System.out.println(s); } } }
23. $ time java ReadAL.java Exception in thread "main" java.lang.OutOfMemoryError: Java heap space … at ReadAL.main(ReadAL.java:8) real 0m32.560s user 1m38.740s sys 0m2.037s
25. for ( String s : (Iterable<String>)Files.lines(Paths.get(
 "gigabyte.txt"))::iterator ) {
27. someObjects.forEach( obj -> { … })
28. someObjects.forEach( obj -> { … // Cannot stop before the last obj! })
29. https://docs.raku.org/routine/lines
30. https://docs.raku.org/routine/lines lines()
31. https://docs.raku.org/routine/lines lines() $string.lines
32. https://docs.raku.org/routine/lines lines() $string.lines $filehandle.lines
33. https://docs.raku.org/type/Seq
34. .say for "gigabyte.txt".IO.lines .grep({ last if /^END/; /^a/ })
35. .say for "gigabyte.txt".IO.lines .grep({ last if /^END/ }).grep(/^a/)
36. for "gigabyte.txt".IO.lines .grep({ /^END/ or last }) { .say if /^a/; }
37. for "gigabyte.txt".IO.lines { last if /^END/; .say if /^a/; }
38. for "gigabyte.txt".IO.lines { last if /^END/; next if !/^a/; .say; }
40. Much Thanks
 to You All!
41. Copyrights
42. Copyright Information: Images and Video • Camelia • © 2009 by Larry Wall
 http://github.com/perl6/mu/raw/master/misc/camelia.txt • Barnyard Dawg and Foghorn Leghorn • © 1946, 1949, 1956 by Warner Bros. • Merrie Melodies: Walky Talky Hawky
 Looney Tunes: Henhouse Henery
 Merrie Melodies: The High and the Flighty
43. Copyright Information: This Talk This work is licensed under a Creative Commons Attribution 4.0 International License. CC BY https://creativecommons.org/licenses/by/4.0/ (email me for the original Apple Keynote .key file)
44. History • v 0.98 2021-07-30
 Test recording, incomplete. Lightning storm. • v 1.00 2021-08-07
 Presented final version to The Raku Conference
 (Previously recorded on 2021-08-06)