|
87
|
1 module Factorial where
|
|
|
2 -- The book says to use "Main", but that now triggers "The IO action ‘main’ is not defined in module ‘Main’". https://optimistictypes.com/compiler-errors/#module-main-where says Main is special and must have a function "main".
|
|
|
3 -- Instead we'll use our own module name, because it doesn't seem to be important (yet).
|
|
|
4
|
|
|
5 -- Without pattern matching
|
|
|
6 fact :: Integer -> Integer
|
|
|
7 -- Note how this is like a Python "x if a else y"
|
|
|
8 fact x = if x == 0 then 1 else x * fact (x - 1)
|
|
|
9
|
|
|
10 -- With pattern matching
|
|
|
11 factorial :: Integer -> Integer
|
|
|
12 factorial 0 = 1
|
|
|
13 factorial x = x * factorial(x - 1)
|
|
|
14
|
|
|
15 -- With guards
|
|
|
16 factorial_guard :: Integer -> Integer
|
|
|
17 factorial_guard x
|
|
|
18 -- List of definitions, which look similar to the pattern matching but without the function name
|
|
|
19 | x > 1 = x * factorial(x - 1)
|
|
|
20 -- And the fallback "otherwise" result
|
|
|
21 | otherwise = 1 |
