stripAnsi is called many times during rendering (by strWidth), so
should be fast. It was originally a regex replacement, and more
recently a custom parser. The parser was slower, particularly the one
in 1.19.1. See #1350, and this rough test:
time118ish = timeIt $ print $ length $ concat $ map (fromRight undefined . regexReplace (toRegex' "\ESC\\[([0-9]+;)*([0-9]+)?[ABCDHJKfmsu]") "") testdata
time119 = timeparser (many (takeWhile1P Nothing (/='\ESC') <|> "" <$ ansi))
time1191 = timeparser (many ("" <$ try ansi <|> pure <$> anySingle))
timeparser p = timeIt $ print $ length $ concat $ map (concat . fromJust . parseMaybe p) testdata
testdata = concat $ replicate 10000
[ "2008-01-01 income assets🏦checking $1 $1"
, "2008-06-01 gift assets🏦checking $1 $2"
, "2008-06-02 save assets🏦saving $1 $3"
, " assets🏦checking ..m$-1\ESC[m\ESC[m $2"
, "2008-06-03 eat & shop assets:cash ..m$-2\ESC[m\ESC[m 0"
, "2008-12-31 pay off assets🏦checking ..m$-1\ESC[m\ESC[m ..m$-1\ESC[m\ESC[m"
]
ghci> time118ish
4560000
CPU time: 0.17s
ghci> time119
4560000
CPU time: 0.91s
ghci> time1191
4560000
CPU time: 2.76s
Possibly a more careful parser could beat regexReplace. Note the
latter does memoisation, which could be faster and/or could also use
more resident memory in some situations.
Ideally we would calculate all widths before adding ANSI colour codes,
so we wouldn't have to wastefully strip them.
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