YouTube user ferlessleedr made a functional Portal gun out of LEGO:
The gun took about a year to plan, three weeks to build, and is just under 2,000 pieces. It has a LEGO Mindstorm controller stuffed inside, so the prongs can be opened and closed via a switch, as well as some light-up effects.
Check it out at Geekologie: Link
I don't think we have the same definition of "functional".
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