[Haskell-cafe] Instantiation problem

Henning Thielemann schlepptop at henning-thielemann.de
Mon Jan 31 00:23:41 CET 2011

Patrick Browne schrieb:
> On 30/01/2011 19:43, Henning Thielemann wrote:
>> I do not see a constant 1 that is equated with a type.
> This is due to my misunderstanding of Haskell.
> After your comments my understanding of the  unit function is as follows:
> 1) In the instance below the argument for unit must have type
> LengthInMetres
>>> instance MetricDescription LengthInMetres Metre where
>>>>  valueInUnit (LengthInMetres d) = d
>>>>  unit l = Metre
> 2) The constant 1 on the LHS can be replaced _ because it is the fact
> that unit is defined in this instance the determines the return value.

Btw. the parameter of 'unit' is a lower-case "L" not a One.

> 3) The RHS is not a type but a constructor.


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