@eq()

The @eq() function takes N strings, and tests if they're all equal. If
they are, it returns "1". If not, "0".
Also, @eq exhibits "short-circuiting": after an unequal argument is found,
the rest of the arguments will not be evaluated.

Usage:
@eq("a", "b")
@eq("%#", "204")
@eq("a", "a", "a")
@eq("", @getfield("%!", "field"), @tell("%#", "Field has been set."))