Haskell list comprehension full#
Haskell list comprehension code#

You should think about switching to sets. If you manage data sets where each object can occur only once If you really need random access, as in the Fourier Transform,

Haskell list comprehension code#

I found the following code (but convoluted in a more specific function) in a Haskell program the elements for which the predicate p is True. If you can write the loop over a data structure once and debug it, then there's no need to duplicate that code.Īnother example: the function count counts the number of elements which fulfill a certain property, i.e. This is a special case of the general principle of separating concerns.

If the last implementation of raise does not show the expected behaviour, you can inspect map (I hope it is correct :-) ) and the invoked instance of ( + ) separately. It may appear in the standard libraries later, or you may later find that it is already there in an even more general way.ĭecomposing a problem this way also has the advantage that you can debug more easily. If you find the function very general, put it in a separate module and re-use it. Thanks to higher order functions Haskell gives you very many opportunities to factor out parts of the code. This helps you and others understand the program. If you don't find appropriate functions in the standard library, extract a general function. But if you use a standard function, the reader will either immediately understand what you've done, or can learn something new.Įxplicit recursion is not generally bad, but you should spend some time trying to find a more declarative implementation using higher order functions.Īnd the reader knows that the complete list is processed and that each output element depends only on the corresponding input element. If you rewrite an existing library function, the reader of your code might spend a minute trying to figure out why you've done that.

Haskell list comprehension full#

The standard libraries are full of useful, well-tuned functions. Instead, you can now add 'this is disputable' on /Discussion and change this page only when some sort of consensus is reached.

We all know this, please don't add 'this is disputable' to each item! We try to derive general rules from them, though they cannot be applied deterministically and are a matter of taste. This page shows several examples of how code can be improved.

7.2 Some Common (and not so common!) Hugs Errors.

7.1 Common Mistakes and Incorrect Beliefs By Haskell Beginners.

6.3 Partial functions like fromJust and head.

5.3 Don't use Int when you don't consider integers.

4.2 Don't ask for the minimum when you don't need it.

4.1 Don't ask for the length of a list when you don't need it.

2.3 Only introduce identifiers you need.