RunBinaryHandler typedef

R RunBinaryHandler <R, T1, T2>(Zone self, ZoneDelegate parent, Zone zone, R f(T1 arg1, T2 arg2), T1 arg1, T2 arg2)

Implementation 

typedef RunBinaryHandler = R Function<R, T1, T2>(Zone self, ZoneDelegate parent,
    Zone zone, R Function(T1 arg1, T2 arg2) f, T1 arg1, T2 arg2);