Ideas on how to implement some list comprehensions

list_comprehensions_good_ideas.groovy

import static groovyfp.categories.Fn.*
import groovyfp.categories.*

/*
a = do
    x <- (1..3)
    y <- ('a','b')
    return (x,y)

a = mdo {
    x << (1..3)
    y << ('a'..'b')
    mreturn { [x, y] }
}

*/

def expr = { x, y -> [x + y] }

def result = 
    list(1,2,3).bind { x -> 
        list('a','b').bind { y ->
            list([expr(x,y)])    
        }
    }
    
result.typedRef.value


/*

m = mlet(x:10,y:20) {
    x + y
}

*/

m = just(10).bind { x ->
        just(20).bind { y ->
            just(x + y)
        }
    }

m.typedRef.value