I'm looking for a way to match multiple lines Parslet. The code looks like this:
rule(:line) { (match('$').absent? >> any).repeat >> match('$') }
rule(:lines) { line.repeat }
However, lines will always end up in an infinite loop which is because match('$') will endlessly repeat to match end of string.
Is it possible to match multiple lines that can be empty?
irb(main)> lines.parse($stdin.read)
This
is
a
multiline
string^D
should match successfully. Am I missing something? I also tried (match('$').absent? >> any.maybe).repeat(1) >> match('$') but that doesn't match empty lines.
Regards,
Danyel.
I think you have two, related, problems with your matching:
The pseudo-character match $ does not consume any real characters. You still need to consume the newlines somehow.
Parslet is munging the input in some way, making $ match in places you might not expect. The best result I could get using $ ended up matching each individual character.
Much safer to use \n as the end-of-line character. I got the following to work (I am somewhat of a beginner with Parslet myself, so apologies if it could be clearer):
require 'parslet'
class Lines < Parslet::Parser
rule(:text) { match("[^\n]") }
rule(:line) { ( text.repeat(0) >> match("\n") ) | text.repeat(1) }
rule(:lines) { line.as(:line).repeat }
root :lines
end
s = "This
is
a
multiline
string"
p Lines.new.parse( s )
The rule for the line is complex because of the need to match empty lines and a possible final line without a \n.
You don't have to use the .as(:line) syntax - I just added it to show clearly that the :line rule is matching each line individually, and not simply consuming the whole input.