pyths.m

output = lay (map show pyths)
pyths = [(a, b, intsqrt (a*a+b*b)) // a <- [3..]; b<-[a+1..]; is_sq (a*a+b*b)]
intsqrt x = entier (sqrt x)
is_sq y = (intsqrt y) ^ 2 = y

Finds all pythagorean triangles (right triangles with integer sides) Note the use of a diagonalising list comprehension, with // instead of | as separator. To see the triangles, say

        output

(3,4,5)
(6,8,10)
(5,12,13)
(9,12,15)
(8,15,17)
(12,16,20)
(15,20,25)
(20,21,29)
(7,24,25)
(10,24,26)
(18,24,30)
(21,28,35)
(16,30,34)
(24,32,40)
(12,35,37)
(15,36,39)
(27,36,45)
(9,40,41)
(30,40,50)
(40,42,58)

..... etc