CODEWITHSUNDEEP
haskell
Bao Thai
Bao Thai

Reputation: 553

error using stream package/data type

I have been stuck with a particular situation. I am not sure what the error even is to be honest.

data Stream a = Cons a (Stream a)
streamToList :: Stream a -> [a]
streamToList (Cons x (Stream xs)) = x: streamToList (Stream xs)

Doing something like this, I got Not in scope : data constructor 'Stream', so I googled the error and some solutions were to change stream to a lower case

data Stream a = Cons a (Stream a)
streamToList :: Stream a -> [a]
streamToList (Cons x xs) = x: streamToList (stream xs)

But then I get Parse error in pattern : stream

I tried importing Data.Stream (googled on Hoogle) but Could not find module 'Data.Stream'

Currently using Haskell from Ubuntu packages

Upvotes: 1

Views: 66

Answers (1)

ephemient
ephemient

Reputation: 205024

streamToList :: Stream a -> [a]
streamToList (Cons x xs) = x : streamToList xs

Stream is the name of a type, so it can be used on the right-hand side of ::. But it is not a data constructor, so it cannot be used as a value or in pattern matches.

Cons is the name of a data constructor, so it can be used as a value or in pattern matches. But it is not a type.

Upvotes: 1

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