Since Groovy 1.8 a convenient memoize() method is added on closures:
// normal closure
def sum = { int x, int y ->
println "sum ${x} + ${y}"
return x + y
}
sum(3, 4)
sum(3, 4)
// prints
// sum 3 + 4
// sum 3 + 4
// memoized closure
def sumMemoize = sum.memoize()
...