From d3e4f8547c098a143f4d37ae090ccc954384a7ea Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Thu, 16 Mar 2023 14:30:50 -1000
Subject: [PATCH] imp: lib: Hledger.Utils.String: more string strippers

added:
strip1Char
stripBy
strip1By

Not used in hledger right now, but useful to offer in our scripting prelude.
---
 hledger-lib/Hledger/Utils/String.hs | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/hledger-lib/Hledger/Utils/String.hs b/hledger-lib/Hledger/Utils/String.hs
index 6edab75c2..14bb92ade 100644
--- a/hledger-lib/Hledger/Utils/String.hs
+++ b/hledger-lib/Hledger/Utils/String.hs
@@ -20,6 +20,9 @@ module Hledger.Utils.String (
  strip,
  lstrip,
  rstrip,
+ strip1Char,
+ stripBy,
+ strip1By,
  chomp,
  chomp1,
  singleline,
@@ -69,6 +72,25 @@ lstrip = dropWhile isSpace
 rstrip :: String -> String
 rstrip = reverse . lstrip . reverse
 
+-- | Strip the given starting and ending character
+-- from the start and end of a string if both are present.
+strip1Char :: Char -> Char -> String -> String
+strip1Char b e s = case s of
+  (c:cs) | c==b, not $ null cs, last cs==e -> init cs
+  _ -> s
+
+-- | Strip a run of zero or more characters matching the predicate
+-- from the start and end of a string.
+stripBy :: (Char -> Bool) -> String -> String
+stripBy f = dropWhileEnd f . dropWhile f
+
+-- | Strip a single balanced enclosing pair of a character matching the predicate
+-- from the start and end of a string.
+strip1By :: (Char -> Bool) -> String -> String
+strip1By f s = case s of
+  (c:cs) | f c, not $ null cs, last cs==c -> init cs
+  _ -> s
+
 -- | Remove all trailing newlines/carriage returns.
 chomp :: String -> String
 chomp = reverse . dropWhile (`elem` "\r\n") . reverse