![]() ![]() Here var 2 is the expression that creates the value in the lists. ![]() An example of list comprehension in Python. Haskell types can be qualified by adding a (possibly empty) list of predicates, or class constraints, to restrict the ways in which type variables are instantiated 4 : data Qual t Pred :> t deriving Eq. List comprehension allows you to create your collection with an expression that exists out of three parts: the output expression, the input sets and the predicates that filter the input set. HASKELL LIST COMPREHENSION GENERATORGhci > factorial :: Int -> Int factorial n = product ghci > factorial 10 - okay, this is fine 3628800 ghci > factorial 100 - (silent) overflow! 0 ghci > factorial :: Integer -> Integer factorial n = product ghci > factorial 100 - woo! works great! 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000 ghci > factorial 10000 - also works fine! so many digits. Assuming that none of these neat data structures existed and the only way to create a data structure was to use closures, this would be the implementation for a list (Python). List comprehension in Haskell is a way to produce the list of new elements from the generator we have passed inside it. ![]()
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