hfor ghc -X extensions

hfor '[ (a,b) | (a:t) <- init $ Data.List.tails [9,2,4,7,5,6], b<-t, a+b==10]'
(4,6)

hfor '[x | x<-[1..20], then take 5]'
hfor '[x*y | x<-[1..5] | y <-[2,4..] ]'
alias tf='tree -f'