With subtree, rule( :result => subtree( :z ) ) will match an array that contains hashes, arrays, etc. With rule( :result => sequence( :z ) ), the array to be matched must only contain simple objects: strings, integers, Objects of any time. In other words, a sequence has no "depth." Make sense?
Then whatever you do in the action block is your business. That's where you take the data that matched and transform it into either your desired output or some intermediate (presumably cleaner) data representation, like an AST. On Wed, May 18, 2011 at 3:23 PM, Thiel Chang <[email protected]> wrote: > Hi Jason, > > As I understand you well does it mean that the array in { :result => [ ... > ] } may not contain hash elements, e.g. [ { :a => "x"}, ..., { :b => "z"} > ] ? > > When I have to use the subtree approach the rule/solution is something > like: > > rule( :result => subtree( :z ) ) { > > z[0].each {|k,v| > > @key = k > > @val = v } > > z[0] = Hash[@key, "newtmp"] > > @ops = [] > > index = 0 > > z[1].each {|hsh| > > hsh.each {|k| @ops[index] = k > > index += 1} > > } > > z.delete_at(1) > > {:result => z} > > } > > Just plain Ruby code. > > > > > > > > Op 18-5-2011 22:46, Jason Garber schreef: > > Oh, I see. In your example, there were hashes in the array, which wouldn't > match a sequence. That would be a subtree. I've see now. > > On Wed, May 18, 2011 at 2:44 PM, Thiel Chang <[email protected]> wrote: > >> Hi Jason, >> >> Many thanks for your response and I will articulate my problem again. >> >> My problem is that I don't understand how to apply the sequence(symbol) in >> a transformation rule. Althought, I saw it in the Parslet examples it is >> still a fuzzy item for me. >> Therefore, I created a problem and in the solution I want to use the >> sequence(symbol), if possible. >> >> Let the expression be: { :result => [{ :w => "a" }, { :x => "b" } , { >> :y => "c", :z => "d"} ] } . So :result => [ ... ] is a hash with >> :result as a key and the array [ ... ] as a value. >> >> I want this expression be transformed into: { :result => [ "imf", >> "strauss", "kahn" ] } :-) >> >> In the Parslet Transformation documentation it is said: "....., but you >> cannot replace the array as a whole. This is the purpose of >> sequence(symbol): sequence(:x) which will match all of these [ 'a', 'b', >> 'c' ] [ 'a', 'a', 'a' ] [ Foo.new, Bar.new ] ... " Besides, >> sequence is very picky about what it consumes and what not. But that's not >> defined in CLEAR way in this documentation and not ILLUSTRATED with >> examples. This part of the documentation is not very didactic. >> >> When I consider this problem as plain Ruby code it is easy to transform >> the code, but that's not the solution I want. My goal to understand the use >> of sequence in a transformation rule. >> >> Cheers, >> >> Thiel >> >> Op 18-5-2011 21:01, Jason Garber schreef: >> >> Thiel, >> :elements gets captured and becomes available in the block's context. If >> you want the output to be a hash, you have to have {:result => element } in >> the block. But then your transformation rule does nothing, so I don't see >> why you'd want to. >> >> I couldn't follow your example very well. Perhaps that's why no one has >> responded yet. Try articulating your problem again if you're still having >> trouble. >> >> Jason >> >> On Wed, May 18, 2011 at 5:55 AM, Thiel Chang <[email protected]> wrote: >> >>> Hi guys, >>> >>> I am still struggling with the transformation rules. :-( >>> >>> My aim is to understand the application of sequence(symbol) in >>> transformation rules. >>> >>> So, I made a simple test to replace an array of objects in a >>> transformation rule. >>> >>> The input tree for Transform is: >>> >>> { :result => [{ :w => "a" }, { :x => "b" } , { :y => "c", :z => "d"} ] >>> } >>> >>> and the transformation rule is: >>> >>> rule( :result => sequence(:elements) ) { puts elements.inspect } >>> >>> The new array is: [ "imf", strauss", "kahn"] >>> >>> The required result should be: { :result => [ "imf", "strauss", "kahn" >>> ] } >>> >>> I would be very glad if anyone can provide the solution(s). >>> >>> Many thanks in advance, >>> >>> Thiel >>> >>> >>> >>> >> >> > >
