fs: ?map
f1: fn1 { * 2 }
f2: fn { n } { * n }
fsf1: fn1 { .fs ?f1 }
fsf2: fn1 { .fs ?f2 }

print fsf1 { 0 1 2 3 }
print fsf2 { 0 1 2 3 }
print fsf1 { 2 4 6 8 }
print fsf2 { 2 4 6 8 }