he Haskell functions div and ^ are partial, meaning they can crash with a so-called imprecise exception (an exception that is not visible in the type, also sometimes called IO exceptions).
partial functions
8 Matching Annotations
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- Aug 2025
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diku-dk.github.io diku-dk.github.io
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We can use newtype whenever we define a datatype with a single constructor that has a single-value - intuitively, whenever we simply "wrap" an underlying type.
Brug gerne newtype når vi bare skal "wrappe" en underliggende datatype (i det her tilfælde Double) med en anden datatype (som her er Q der er vores value constructor til højre for =)
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Note that we do not actually use the type parameter unit in the right hand side of the definition. It is a phantom type, that exists only at compile-time, in order to constrain how Qs can be used. When constructing a value of type Q, we can instantiate that unit with anything we want. For example
Vigtig: forklaring af phantom type
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Specifically, we now define a type constructor Q for representing a quantity of some unit:
Fra Learn You Haskell...: "Once again, it's very important to distinguish between the type constructor and the value constructor. When declaring a data type, the part before the = is the type constructor and the constructors after it (possibly separated by |'s) are value constructors." Så Q til vnstre er type constructoren med type parameteret unit, og Q til højre er valu constructor, som tager en Double
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irst, we define some types that do not have constructors:
Husk at value constructors for en type er til højre for =
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ee how the fmap method turns an f a into an f b, intuitively changing the a values to b values. That means f by itself is not a type - it must be applied to a type, and hence is a type constructor.
Faktisk rigtig fin forklaring for at forstå forskel på type og type constructor
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One interesting detail is that Functor instances are not defined for types, but for type constructors. Se
Vigtigt!
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import Test.Tasty (defaultMain)
Her importerer vi kun defaultMain funktionen fra modulet
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