Re: [commit: base] master: fix negative numbers for * modifiers (#7457) (63202b9)

On Mon, Jan 28, 2013 at 02:06:48AM -0800, Simon Marlow wrote:

commit 63202b9df64041e1c17603ad5f06fec3c51f357d Author: Simon Marlow Date: Mon Jan 28 09:38:06 2013 +0000

fix negative numbers for * modifiers (#7457)

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Text/Printf.hs | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/Text/Printf.hs b/Text/Printf.hs index 0546e84..6028e16 100644 --- a/Text/Printf.hs +++ b/Text/Printf.hs @@ -281,7 +281,7 @@ getSpecs l z s ('*':cs) us = in ((p', r), us''') '.':r -> (stoi 0 r, us') _ -> ((-1, cs), us') - in (n, p, l, z, s, cs'', us'') + in (abs n, p, if n < 0 then not l else l, z, s, cs'', us'') getSpecs l z s ('.':cs) us = let ((p, cs'), us') = case cs of

Hmm, this works for minBound for Int8: > printf "%*sx\n" (-4 :: Int8) "hi" hi x > printf "%*sx\n" (minBound :: Int8) "hi" hi x but not Int: > printf "%*sx\n" (-4 :: Int) "hi" hi x > printf "%*sx\n" (minBound :: Int) "hi" hix (the last line should have a huge number of spaces between "hi" and "x". Actually, this matches what the printf commandline program does: $ printf "%*sx\n" -4 hi hi x $ printf "%*sx\n" -2147483648 hi hix and C just doesn't print anything: $ cat q.c #include int main(void) { int i; i = -2147483648; printf("%*sx\n", -4, "hi"); printf("%*sx\n", i, "hi"); printf("Test\n"); return 0; } $ gcc q.c -o q $ ./q hi x Test $ This probably isn't important for printf, but it's a problem that seems to keep coming up. I wonder if there's something we should do. We could add methods like maybeAbs :: a -> Maybe a maybeAbs = Just . abs -- default method to Num, but div and friends are a little trickier, as they can return either divZeroError or overflowError, or even partially succeed in the case of (-1) `divMod` minBound == (overflowError, 0) Thanks Ian