Translator – Reference Mode

A new token mode is needed for the INPUT commands. The current token modes are command, assignment, assignment list and expression. Consider these invalid INPUT statements:

INPUT A+B*C
INPUT A+B*C$

The INPUT commands must have variables, not expressions. If expression mode was used, at each comma and the end of the statement, the INPUT command handler would need to check the token on top of the done stack to see if its reference flag is set. The first statement above, the INPUT command handler will see the multiplication token on top of the stack. Its first token will be A and last token will be C. An “expecting variable” error would be reported pointing to the whole A+B*C expression. This would be acceptable.

However, in the second statement, an error occurs before the INPUT command handler gets a chance to report an error. When the multiplication token checks its second operand, it will report an “expecting numeric expression” error pointing at the C$ token. This would make no sense. The proper error for both of these statements would be an “expecting semicolon, comma or end-of-statement” error pointing at the add token.

The new reference mode will only accept variables and array elements, specifically tokens with no parentheses and tokens with parentheses. If these tokens turn out to be user functions, which the Translator cannot determine, the error will be reported by the Encoder. Reference mode will be set when the INPUT command is received and after the comma or semicolon of the prompt string expression of the INPUT PROMPT command. It will also be used later for the READ command.

In reference mode, internal functions, define functions, and unary operators will be reported as invalid (“expecting variable” error). After the variable or array element token is pushed to the done stack, the state will be set to end expression so that only end expression tokens are valid. Binary operators will then be correctly be reported as invalid.

While reference mode was being implemented, some more problems were found in the Translator code...