Ketil Malde wrote:

Maurício writes:

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Couldn't match `Float' against `Complex Float' Expected type: Float Inferred type: Complex Float In the second argument of `(+)', namely `sqr_delta' In the definition of `x1': x1 = (b + sqr_delta)

The error message says it all, really.

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Note that Haskell doesn't automatically convert arguments for you -- this is a feature.

-kzm

When I type this: ***** import Complex; a = 3 :+ 4; ***** and load it into ghci, "a + 4" gives me "7.0 :+ 4.0", although "a + (4::Float)" gives me that error again. Why Haskell converts "4" to Complex but not a Float? Maurício

On Thu, 6 Jan 2005 karczma@info.unicaen.fr wrote:

Actually this is not a "conversion", but an overloading of numerical constants. The lexical entity "4" behaves as "fromInteger 4", and the type checker uses the fromInteger appropriate to the context. Floating, Complex, etc. With 4.0 it will work also (overloaded fromRational).

Though I think the syntax should distinguish between the polymorphic value '4' and the bare integer from which it is convert, say '#4', that is '4 = fromInteger #4'.

Jules Bean wrote:

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(...) Why Haskell converts "4" to Complex but not a Float?

The answer lies available to you in ghci:

Prelude> :t 4 4 :: forall t. (Num t) => t

The type of for is 'any type in the Num class'. So '4' stands for the Integer four as well as the Float four and the Double four and indeed the Complex 4.

No conversion is actually happening.

Interesting. The tutorial I'm following didn't say anything about classes yet. I'll read about it and then go back to my problem. Thanks.