||this generates all solutions to the 8 queens problem -- say
||      solns
||and it will print the solutions one per line - all 92 of  them.   This
||is  a  good  program  for testing the garbage collector.  Say `/gc' to
||switch on garbage collector diagnostics.

solns = layn(map show (queens 8))
queens 0 = [[]]
queens (n+1) = [q:b|b<-queens n;q<-[1..8];safe q b]
safe q b = and[~checks q b i|i<-index b]
checks q b i = q=b!i \/ abs(q-b!i)=i+1

||Note that the function `queens n' returns a list of all  solutions  to
||the n queens problem (placing queens in the first n columns of a chess
||board, so that no queen gives check  to  another).   A  board  with  n
||queens  is represented as a list of n numbers, namely the positions of
||the queens in each column

||This  example  exhibits  a  basic   technique   of   lazy   functional
||programming,  which is to eliminate backtracking from a search problem
||by working at the level of a list of  all  solutions,  rather  than  a
||single solution.