That helps, but: #include #include int main () { long double d = HUGE_VAL; printf("%.30Lf\n", d); } still prints just (as it should, I think): inf Is there maybe some way to check if a double or long double do have a "proper" value?

You probably want something like printf("%.10Lg",d);. Here's a shot C example and its output:

#include

int main(int argc, char * argv[]) { long double d = 0.123456789;

printf("%.30Lf\n", d); printf("%.20Lg\n", d); printf("%.20Le\n", d); }

/* 0.123456788999999997336054491370 0.12345678899999999734 1.23456788999999997336e-01 */

On Fri, Jul 17, 2009 at 6:41 PM, Maurí­cio wrote:

...

When we printf doubles from C (like when using hsc2hs to bind to a constant) we can get something that's not valid Haskell. See these 2 examples:

3.40282347e+38F

inf

Do you know some way to printf a double using printf (or any other standard function) that's always going to give me valid Haskell text, even in special cases?

Thanks, Maurício

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Brandon S. Allbery KF8NH wrote:

On Jul 17, 2009, at 22:27 , Maurí cio wrote:

...

Is there maybe some way to check if a double or long double do have a "proper" value?

isNaN :: a -> Bool True if the argument is an IEEE "not-a-number" (NaN) value

isInfinite :: a -> Bool True if the argument is an IEEE infinity or negative infinity

isDenormalized :: a -> Bool True if the argument is too small to be represented in normalized format

isNegativeZero :: a -> Bool True if the argument is an IEEE negative zero

isIEEE :: a -> Bool True if the argument is an IEEE floating point number

(in Prelude, even. Class RealFloat)

But don't trust the Prelude in Hugs (Sept2006)! The isInfinite and isNaN methods are hard-coded to answer False, ignoring the argument entirely. The logfloat package has the module Hugs.RealFloat[1] which provides correct versions (defaulting to the Prelude definitions for non-Hugs compilers). [1] http://hackage.haskell.org/packages/archive/logfloat/0.12.0.1/doc/html/Hugs-... -- Live well, ~wren