[Haskell-cafe] Outstanding context : (Num b, Random b)

2004-02-26 Thread horsh 


Hi,

I am very new to haskell.

Could anyone please explain why these two things are not equivalent:

m2 = do  a - (drawInt 1 10)
 print a
drawInt :: Int - Int - IO Int
drawInt x y = getStdRandom (randomR (x,y))

m1 = do b - getStdRandom (randomR (1,10))
print b

the second one produces
*** Binding : m1
*** Outstanding context : (Num b, Random b)

in Hugs.

thanks
horsh

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Re: [Haskell-cafe] Outstanding context : (Num b, Random b)

2004-02-26 Thread Glynn Clements 

horsh  wrote:

 I am very new to haskell.
 
 Could anyone please explain why these two things are not equivalent:
 
 m2 = do  a - (drawInt 1 10)
print a
 drawInt :: Int - Int - IO Int
 drawInt x y = getStdRandom (randomR (x,y))
   
 m1 = do b - getStdRandom (randomR (1,10))
   print b
 
 the second one produces
 *** Binding : m1
 *** Outstanding context : (Num b, Random b)

In Haskell, numeric literals are overloaded. 1 could be an Int,
Integer, Rational, Float etc. randomR can use any of Int, Integer,
Float or Double, but it needs to know which. Adding an explicit type
signature to one of the literals will eliminate the error, e.g.:

m1 = do b - getStdRandom (randomR (1,10 :: Int))
print b

-- 
Glynn Clements [EMAIL PROTECTED]
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Re: [Haskell-cafe] Outstanding context : (Num b, Random b)

2004-02-26 Thread Ketil Malde 
horsh  [EMAIL PROTECTED] writes:

 Could anyone please explain why these two things are not equivalent:

One of them has a type signature?

-kzm
-- 
If I haven't seen further, it is by standing in the footprints of giants
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