[Haskell-cafe] Re: Has anybody replicated =~ s/../../ or even something more basic for doing replacements with pcre haskell regexen?

Thomas Hartman tphyahoo at gmail.com
Tue Mar 17 15:15:57 EDT 2009

2009/3/16 ChrisK <haskell at list.mightyreason.com>:
> Let me open the discussion with all the questions I can quickly ask:
>  What should the "subRegex" function do, exactly?
>  (Single replacement,global replacement,once per line,...)

Try to do the same thing as =~ s/../../ in perl.

For a version 1: Global replacements, don't treat newlines separately,
^ and $ anchor at start and end of string.

There could be a Bool option to support multiline replacement modes.

>  What should the replacement template be able to specify?
>  (Can it refer to all text before a match or all text after?)
>  (Can it access the start/stop offsets as numbers?)

Again, follow =~ s/../../

I'm not sure what =~ allows in this dimension though.

My instinct is

> (Can it refer to all text before a match or all text after?)


>  (Can it access the start/stop offsets as numbers?)


But maybe that's just because I've never needed the above functionality.

I basically think of =~ s as "quick cleanup for dirty text" solution,
nothing approaching full-fledged parsing.

>  Should the replacement template be specif~ied in a "String"?

Sure, just like it is in Text.Regex.subRegex now. No combinators,
\numbered capture references are fine.

> As an abstract
> data type or syntax tree?  With combinators?

Just a string I think.

>  What happens if the referenced capture was not made?  Empty text?

Return the original string. Isn't that what subRegex already does?

>  How will syntax errors in the template be handled (e.g. referring to a
> capture that does not exist in the regular expression)?

runtime error

>  Will the output text be String? ByteString? ByteString.Lazy? Seq Char?
>  Note: String and Strict Bytestrings are poor with concatenation.

String. Add support for others if users holler for it

>  Can the output text type differ from the input text type?


My 2c.

> --
> Chris
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