maybe_nil := if yes
    "safe"
else nil
say "maybe: $maybe_nil"
x := maybe_nil or fail "Oh no!"
say x

say "or: $(yes or fail "Whoops")"
say "or: $(nil or maybe_nil or fail "Whoops")"
say "and: $(no and fail "Drat")"
maybe_nil = nil
say "and: $(maybe_nil and "unsafe" and fail "Drat")"