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Parser Combinators Beat Regexes

(entropicthoughts.com)
122 points mooreds | 2 comments | 4/9/2025, 9:53:00 PM | HN request time: 0.529s | source
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DadBase ◴[4/10/2025, 1:55:00 AM] No.43639894[source]▶

Parser combinators are great until you need to parse something real, like CSV with embedded newlines and Excel quotes. That’s when you reach for the reliable trio: awk, duct tape, and prayer.

replies(2): >>43640949 #>>43640977 #
iamevn ◴[4/10/2025, 5:38:00 AM] No.43640977[source]▶

I don't follow why parser combinators would be a bad tool for CSV. It seems like one would specify a CSV parser as (pardon the pseudocode):

  separator = ','
  quote = '"'
  quoted_quote = '""'
  newline = '\n'
  plain_field = sequence(char_except(either(separator, quote, newline)))
  quoted_field = quote + sequence(either(char_except(quote), quoted_quote)) + quote 
  field = either(quoted_field, plain_field)
  row = sequence_with_separator(field, separator)
  csv = sequence_with_separator(row, newline)

Seems fairly natural to me, although I'll readily admit I haven't had to write a CSV parser before so I'm surely glossing over some detail.

replies(2): >>43641113 #>>43643933 #
1. kqr ◴[4/10/2025, 6:04:00 AM] No.43641113[source]▶

I think GP was sarcastic. We have these great technologies available but people end up using duct tape and hope anyway.

replies(1): >>43643935 #
2. DadBase ◴[4/10/2025, 2:09:00 PM] No.43643935[source]▶

Exactly. At some point every parser combinator turns into a three-line awk script that runs perfectly as long as the moon is waning and the file isn’t saved from Excel for Mac.