In Python I can use locale.format
to pretty-print numbers according to locale setting:
>>> import locale
>>> locale.setlocale(locale.LC_ALL, "en_US.UTF-8")
'en_US.UTF-8'
>>> locale.format("%.2f",1234567.89,grouping=True)
'1,234,567.89'
How can I do the same in Haskell? I see that there are localeconv and setlocale bindings, but is there a generic pretty printer which respects Lconv
?
I would say that if the library in question is missing then you could either write yourself one (obvious option, not easy) or write a binding for the needed function. For example, restricted binding for sprintf
which allows to sprintf only doubles:
Double.hs:
{-# INCLUDE "double.h" #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module Double (cPrintf) where
import Foreign
import Foreign.C.Types
import System.IO.Unsafe
import qualified Data.ByteString as B
foreign import ccall "double.h toString"
c_toString :: CDouble -> (Ptr Word8) -> CInt -> IO CInt
buf = unsafePerformIO $ mallocBytes 64
cPrintf :: Double -> B.ByteString
cPrintf n = B.pack $ unsafePerformIO $ do
len <- c_toString (realToFrac n) buf 64
peekArray (fromIntegral len) buf
double.h:
int toString(double a, char *buffer, int bufferLen);
double.c:
#include <stdio.h>
#include "double.h"
int toString(double a, char *buffer, int bufferLen) {
return snprintf(buffer, bufferLen, "%f", a);
}
Build as:
gcc -c double.c
ghc --make Main.hs double.o