BBC BASIC equivalent of the 'spaceship' operator

[Richard Russell]

When translating code from another language to BBC BASIC you may occasionally encounter the so-called spaceship operator <=>; languages which have this three-way comparison operator include Perl, Ruby, PHP and C++.

There's a straightforward conversion to BBC BASIC: a <=> b is equivalent to SGN(a - b).

For example in PHP you might have:

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echo x <=> y;

In BBC BASIC this would be:

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PRINT SGN(x - y)

[Richard Russell]

There's a straightforward conversion to BBC BASIC: a <=> b is equivalent to SGN(a - b).

The Wikipedia article correctly points out that if you are extremely unlucky you may have a pair of numbers a, b which can be legitimately compared but when subtracted may result in an overflow (and hence an error being reported). If this is a concern an alternative BBC BASIC formulation of a <=> b is (a < b) - (a > b).

In PHP:

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echo x <=> y;

In BBC BASIC (method 1):

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PRINT SGN(x - y)

In BBC BASIC (method 2):

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PRINT (x < y) - (x > y)

This alternative method can't be used if a and/or b are expressions containing function calls which may have side-effects, since they will be called twice.