Language – INPUT command (Change)

As the translation of the INPUT command was being designed, a serious flaw was uncovered with the current syntax. This can be shown with an example. Say there is a user function named Prompt$ that takes a single argument, in other words FUNCTION Prompt$(Index). The intention is to use this function as the prompt string expression in an INPUT statement, which looks like this (using the comma separator to suppress the addition of the default question mark prompt):

INPUT Prompt$(I),Array(I)

To the Translator, the Prompt$ is a token that has a parentheses, which could be either an array or a user function. Requiring parentheses to be inserted around Prompt$(I) to force it to be detected as a prompt expression instead of a variable is not acceptable. The translation of the above is different depending on whether it is an array or a user function:

Array:  INPUT'Question' I Prompt$(<ref> InputStr I Array(<ref> InputDbl Input
Function:  I Prompt$( INPUT'Prompt+Question' I Array(<ref> Input Dbl Input'Tmp'

These two translations are radically different, so one can't assumed and then changed later by the Encoder when it has determined whether it is an array or a function. The Translator needs to know whether it is a prompt or not. If it knows that it is a prompt, then it does not need to know whether it is an array or a function (the translations are the same). For a semicolon, this is not an issue because the item before semicolon is a prompt (unless it is at the end of the line).

To resolve this issue, there are two alternatives. Either the comma separator be eliminated (where a semicolon only indicates a prompt and suppresses the “? ” leaving no way to add the “? ” except to actually add it to the prompt – not desirable), or use the ANSI BASIC syntax of the PROMPT keyword to indicate a prompt string expression follows. The latter will be used and the functionality of the comma (no “? ”) and semicolon (add “? ”) will remain.

Using the PROMPT keyword is the more logically because it clearly shows that there is a prompt, and this keeps with the spirit of a beginner's language (which is probably why it is part of ANSI BASIC). Therefore the syntax of the INPUT statement will now be:

INPUT [PROMPT <string-expression> {,|;}] <variable>[,<variable> ...][;]

Next, how this will affect the resulting translation and execution of the INPUT statement...