如何根据Haskell的区域设置格式化数字？ [英] How to format numbers according to locale in Haskell?

问题描述

在Python中，我可以使用 locale.format 根据区域设置漂亮地打印数字：

 >>>导入区域设置
>>> locale.setlocale（locale.LC_ALL，en_US.UTF-8）
'en_US.UTF-8'
>>> locale.format（％。2f，1234567.89，grouping = True）
'1,234,567.89'
  

<我怎样才能在Haskell中做同样的事情？我看到有 localeconv和setlocale 绑定，但是有一个通用的漂亮打印机，它尊重 Lconv ？

解决方案

我会说，如果缺少库，那么你可以自己写一个（明显的选择，不容易）或为所需的函数写一个绑定。例如， sprintf 的限制绑定仅允许sprintf加倍：

Double.hs：

  { - ＃INCLUDEdouble.h＃ - } 
 { - ＃LANGUAGE ForeignFunctionInterface＃ - } 
 module Double （cPrintf）其中
 
导入外部
导入Foreign.C.Types 
导入System.IO.Unsafe 
将限定的Data.ByteString导入为B 
 
 foreign import ccalldouble.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 
  
 
 
 
 $ p $ $ $ $ $ $ $ $ toString（double a，char * buffer，int bufferLen）; 
  

double.c：

  #include< stdio.h> 
 #includedouble.h
 
 int toString（double a，char * buffer，int bufferLen）{
 return snprintf（buffer，bufferLen，％f，a ）; 
 
 $ / code $ 
 
 $ b 
构建为：
  gcc -c double.c 
 ghc --make Main.hs double.o 
  
 
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?
解决方案
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


                        
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