The engine is responsible for all the low-level parsing of an input line (i.e., player command).
Upon receiving an input, the engine parses the line into separate words, storing them in the word array.
The word array — i.e., that which is referenced in a Hugo program via word[n] — is an internal structure coded using the word token instead of array#.
A static, read-only parser string called parse$ is used for storage of important data, such as a parser-error-causing word/phrase that cannot otherwise be communicated as an existing dictionary entry.
The first parsing pass also does the following:
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Allows integer numbers for -32768 to 32767.
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Time given in “hh:mm” (hours:minutes) format is converted to an integer number representing the total minutes since midnight, i.e., through the formula: hh * 60 + mm. The original “hh:mm” is stored in
parse$. -
Up to one word (or set of words) in quotation marks is allowed; if found, it is stored in
parse$. -
Special words are processed, i.e., removals and user-defined punctuation are removed, compounds are combined, and synonyms are replaced.[1]
If a user-defined Parse routine exists (i.e., if bytes $1D-1E in the header are not $0000), it is called next.
If the routine returns true, the engine parsing routine is called a second time to reconcile any changes to the word set.
If at any point the parser is unable to continue, either because an unknown word — one not found in the dictionary table — is found, or because there is a problem later, in grammar matching (described below), a parser error is generated, and parsing is stopped. (The unknown or otherwise problem-causing word is stored in parse$.)
The engine has a set of standard parser errors that may be overridden by a user-provided ParseError (i.e., if bytes $1F-20 in the header are not $0000).
If there is no ParseError routine, or if ParseError returns false, the default parser error message is printed.