From eb6baac6e7d16e1547505cbcc1210b9268f72b04 Mon Sep 17 00:00:00 2001
From: Simon Michael <simon@joyful.com>
Date: Mon, 30 Jul 2018 11:04:33 +0100
Subject: [PATCH] lib: make applyN more robust (#852)

---
 hledger-lib/Hledger/Utils.hs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/hledger-lib/Hledger/Utils.hs b/hledger-lib/Hledger/Utils.hs
index 41fb48129..47f49551a 100644
--- a/hledger-lib/Hledger/Utils.hs
+++ b/hledger-lib/Hledger/Utils.hs
@@ -129,9 +129,12 @@ isLeft _        = False
 isRight :: Either a b -> Bool
 isRight = not . isLeft
 
--- | Apply a function the specified number of times. Possibly uses O(n) stack ?
+-- | Apply a function the specified number of times,
+-- which should be > 0 (otherwise does nothing).
+-- Possibly uses O(n) stack ?
 applyN :: Int -> (a -> a) -> a -> a
-applyN n f = (!! n) . iterate f
+applyN n f | n < 1     = id
+           | otherwise = (!! n) . iterate f
 -- from protolude, compare
 -- applyN :: Int -> (a -> a) -> a -> a
 -- applyN n f = X.foldr (.) identity (X.replicate n f)
@@ -218,4 +221,4 @@ mapM' f = sequence' . map f
 tests_Hledger_Utils :: Test
 tests_Hledger_Utils = TestList [
     tests_Hledger_Utils_Text
-    ]
\ No newline at end of file
+    ]