Editing Locomotive BASIC (section)

=== Two missed opportunities? ===
BBC Basic uses a clever method for handling some integer variables, which despite claims of its heavy influence on Locomotive BASIC (and by extension Amstrad BASIC), was not replicated in the latter. BBC BASIC has a 54-byte table reserved for the values of the 27 single letter integers <code>@%, A%, B% ... Z%</code> so they do not occupy nor require lookup in the variable table - a simple left-shift and addition is all that is required to determine the value of a given variable. This makes access to the subject variables very fast and considering their ubiquitous nature, it is perhaps, surprising this mechanism was not used in Amstrad BASIC.

For strings, the descriptor is three bytes in the variable table, made up of a length descriptor and a further (little-endian) address of the actual payload. Had the value returned by @ been the two byte address in the heap (and the length prefix moved to the heap also) this would have substantially reduced access time by replacing the two address lookups with just one.

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Variable table structure for strings.