#

AITON Chapter 1

Adding numbers

⇲ Add the odd numbers between $1$ and $30\:$, i.e., what is $1 + 3 + 5 + \cdots + 25 + 27 + 29

sum [1,3..30]

:{
addOdd 
:}

sum [1..21]

Create a list of square numbers

[(^2) x | x <- [1..10]]

[1,4,9,16,25,36,49,64,81,100]

or

map (^2) [1..10]

[1,4,9,16,25,36,49,64,81,100]

Sum the first ten square numbers

sum [(^2) x | x <- [1..10]]

triangular n = sum [1..n]

map triangular [1..10]

[1,3,6,10,15,21,28,36,45,55]

@@html:<span class=”fraktur”><script src=”https://gist.github.com/lattenwald/bc97a668641df7e77ef0.js”>@@ @@html:</script></span>@@

triangleNumsAlt = map (\i -> i * (i+1) `div` 2) [1..]

take 10 triangleNumsAlt

[1,3,6,10,15,21,28,36,45,55]

:{
triangleNums = map fst triangleNums'
  where
    triangleNums' = (1, 2) : map (\(n, i) -> (n+i, i+1)) triangleNums'
:}

take 10 triangleNums

[1,3,6,10,15,21,28,36,45,55]