Isbn Verifier in Haskell
Check if a given string is a valid ISBN-10 number.
exercism fetch haskell isbn-verifier
The ISBN-10 verification process is used to validate book identification
numbers. These normally contain dashes and look like:
The ISBN-10 format is 9 digits (0 to 9) plus one check character (either a digit or an X only). In the case the check character is an X, this represents the value '10'. These may be communicated with or without hyphens, and can be checked for their validity by the following formula:
(x1 * 10 + x2 * 9 + x3 * 8 + x4 * 7 + x5 * 6 + x6 * 5 + x7 * 4 + x8 * 3 + x9 * 2 + x10 * 1) mod 11 == 0
If the result is 0, then it is a valid ISBN-10, otherwise it is invalid.
Let's take the ISBN-10
3-598-21508-8. We plug it in to the formula, and get:
(3 * 10 + 5 * 9 + 9 * 8 + 8 * 7 + 2 * 6 + 1 * 5 + 5 * 4 + 0 * 3 + 8 * 2 + 8 * 1) mod 11 == 0
Since the result is 0, this proves that our ISBN is valid.
Given a string the program should check if the provided string is a valid ISBN-10. Putting this into place requires some thinking about preprocessing/parsing of the string prior to calculating the check digit for the ISBN.
The program should be able to verify ISBN-10 both with and without separating dashes.
Converting from strings to numbers can be tricky in certain languages.
Now, it's even trickier since the check digit of an ISBN-10 may be 'X' (representing '10'). For instance
3-598-21507-X is a valid ISBN-10.
Generate a valid ISBN-13 from the input ISBN-10 (and maybe verify it again with a derived verifier).
Generate valid ISBN, maybe even from a given starting ISBN.
For installation and learning resources, refer to the exercism help page.
Running the tests
To run the test suite, execute the following command:
If you get an error message like this...
No .cabal file found in directory
You are probably running an old stack version and need to upgrade it.
Otherwise, if you get an error message like this...
No compiler found, expected minor version match with... Try running "stack setup" to install the correct GHC...
Just do as it says and it will download and install the correct compiler version:
If you want to play with your solution in GHCi, just run the command:
Feedback, Issues, Pull Requests
The exercism/haskell repository on GitHub is the home for all of the Haskell exercises.
If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!
Converting a string into a number and some basic processing utilizing a relatable real world example. https://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digit_calculation
Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.