Can it write an interpreter without building the tree of parse?

Jeff Zaroyko jeffzaroyko at
Fri Oct 16 19:39:09 EDT 2009

On Fri, Oct 16, 2009 at 12:33 AM, Daneel Yaitskov
<rtfm.rtfm.rtfm at> wrote:
> I want to write a interpreter which does actions (IO) inside the parse
> function. But I don't know how to do it. That code show that What I need.
> Does trick exist that the block function can contain an action (putStr)?

IO actions inside the parse function? I don't think you should want to
do this, what may work better is to have a parse function which
consumes part of the input, producing a value representing as much as
you're willing to interpret, along with the rest of the input.  You
can use Parsec's getInput function for this.  eg:

get1 = do token <- instruction
          remaining <- getInput
          return (remaining,token)


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