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Failure index for negative lookahead in the wrong place? #169

lihaoyi opened this Issue Oct 4, 2017 · 0 comments


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lihaoyi commented Oct 4, 2017

@ import fastparse.all._
import fastparse.all._

@ val p = P( "hello" ~ !"  " ~ AnyChar ~ "world" ).!
p: Parser[String, Char, String] = Capturing(
  Rule("p", ammonite.$sess.cmd1$$$Lambda$1922/1117747481@53abfc07)

@ p.parse("hello  world")
res2: Parsed[String, Char, String] = Failure(
  Not(ElemLiteral(' ')),
  Extra(hello world, [traced - not evaluated])

I'd expect the above Failure object to have an index of 5, since "hello" is 5 characters long, and that's where the Not(ElemLiteral(' ')) call tries to parse and fails. However, it is instead 7, which is where the inner ElemLiteral(' ') call parses and succeeds. It should probably be 5 in this case

@lihaoyi lihaoyi closed this Oct 18, 2018

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