[Dewie]

GForth uses 0 for 'false' but -1 for 'true'... that confuses me a lot.

[kybernetikos]

I expect that it's because in twos complement representation -1 is represented as all bits set.

[IanCal]

I suppose it's because then it can just compare the first bit.

[dlitz]

BASIC does that, too.