A NullSafe Monad in Groovy with Java 8

gistfile1.txt

import java.util.function.Function // requires Java 8

class NullSafe<T> {
    protected final T t
    protected NullSafe(T t) {this.t = t}
    
    static NullSafe<T> enter(T t) { new NullSafe<T>(t) } // enter or "return" is like a constructor
    
    // in the general case, applicative would have the type Function<T, NullSafe<T>> but we don't need that here
    NullSafe<T> rightShift (Function<T,T> applicative) {
        T result = applicative.apply(t)   // here comes the Monad-specific binding logic
        if (result == null) return this   // in our case: ignore the nulls
        enter(result)
    }
}

NullSafe.enter("")   >> // we cannot guarantee null safety for the intial value
    { "Hello "     } >> 
    { it * 2       } >> 
    { it + "World" } >> 
    { println it   } >> // this returns null but we can proceed anyway
    { it + "!"     } >>
    { println it        // there is no other way to get onto the value then being in the Monad! 
      NullSafe.enter it }  // not needed in our special case but better be a good citizen.