[Haskell-beginners] Parsec Many Mishap

[Walter Askew]

I am trying to use parsec to turn strings like this:

“#newch The Period #txt It was the best of times #newpar #txt it was the worst of times”

into data structures like this:

[NewChapter “The Period”, Text "It was the best of times”, NewParagraph, Text "it was the worst of times”]

My current attempt returns this, however:

[NewChapter "The Period "]

That is, my current implementation only parses out the first item in the string and does not find the remaining items.
I’m not sure why that is.  I’d suspect I am misusing parsec’s “many” or “manyTill” somehow, but it isn’t clear to me why my use of “many" results in only single item lists.

My code is pasted below — any suggestions?  This is my first exploration of parsec, so any general suggestion on using the library are welcome (for instance, I do note that I end up double-parsing the strings “#newch, #txt and #newpar because both nextCommand and the newChapter newText and newPar parsers all parse those same strings, but I’m not sure how to avoid that elegantly.)

Thanks for your help!


parser = many command

command = newChapter <|> newTxt <|> newPar

newChapter = do
  try (string "#newch")
  spaces
  chapterName <- text
  return (NewChapter chapterName)

newTxt = do
  try (string "#txt")
  spaces
  content <- text
  return (Text content)

newPar = do
  try (string "#newpar")
  spaces
  return NewParagraph

text = manyTill anyChar nextCommand

nextCommand = try (string "#newch")
              <|> try (string "#txt")
              <|> try (string "#newpar")
              <|> eof *> return ""