Glossary

Project-specific vocabulary, in one place so other pages can use the terms without parenthetical re-definition. Cross-referenced from prose with the :term: role.

abbreviation

A keyword typed as a prefix followed by . — P. for PRINT, F. for FOR. The tokeniser accepts the shortest prefix that resolves unambiguously in the ROM’s keyword order. The de-tokeniser always expands abbreviations to the full keyword, so a round-trip through both normalises them.

Acorn character set

The BBC Micro’s 8-bit character encoding, registered by oaknut.file as the acorn text codec. It differs from ASCII mainly above &7F and in a few low positions (the pound sign is &60). String literals and REM text in a BASIC program are stored in this set; the CLI’s --encoding option bridges it to UTF-8 for host editing.

AUTO

The BBC’s automatic line-numbering mode: it prompts with an ascending line number before each line you type. oaknut-basic reproduces it as the number command and the --start / --step options on tokenise.

BBC BASIC II

The second revision of Acorn’s BASIC interpreter, shipped in the BBC Micro’s 16 KB language ROM. oaknut.basic reproduces this version’s tokeniser and de-tokeniser exactly. Later versions (BASIC IV on the Master, BASIC V on the Archimedes) keep the scheme but change token values; BASIC V additionally uses multi-byte tokens, which BBC BASIC II does not.

crunch

Acorn’s name for the routine that tokenises a line of input — the lexical pass that recognises keywords and packs the line. The oaknut.basic tokeniser reproduces its behaviour, including its start-of-statement and line-number “armed” state.

de-tokenising

Converting a stored, tokenised program back into a source-text listing — what the BBC’s LIST command does. Tokens expand to their keyword spelling and encoded line-number references decode back to plain decimal.

line-number token

The byte &8D, which introduces a three-byte encoded line-number reference inside a program body (after GOTO, THEN, GOSUB, …). The encoding lifts the value clear of &0D so a reference can never be mistaken for a line terminator. Not a keyword token: the tokeniser produces it and the de-tokeniser special-cases it.

pseudo-variable

A keyword that is both readable and assignable — PAGE, PTR, TIME, LOMEM, HIMEM. Each tokenises to its function form when read as a value and its assignment form at the start of a statement, so the byte differs by context.

token

A single byte in the range &80–&FF standing in for a BASIC keyword (&F1 is PRINT, &E5 is GOTO). BBC BASIC II has 126 keyword tokens; a handful of pseudo-variable keywords carry two, one for each of their function and assignment forms.

tokenising

Converting BBC BASIC source text into the compact byte form the interpreter stores and runs. Keywords become single-byte tokens, leading line numbers move into each line’s header, and referenced line numbers are encoded with the line-number token. The inverse is de-tokenising.