Translator – Error Handling (Corrected)

Between working on the development of the INPUT command this week, some time was spent on working out the remaining error reporting issues. Three major areas needed additional checks to report the desired errors:

1. Internal functions not inside expressions, except for functions that return a sub-string  (which can be used in assignments) – this was an issue because the Translator would allow internal functions in assignments, but only the sub-string functions are allowed.
2. At the end of an expression if the mode is assignment, checks were added to see if the Translator was inside an array or sub-string function – this was an issue because the Translator was in expression mode for the subscripts/arguments, but the errors were related to the assignment, therefore the count stack was checked to determine the current situation.
3. There were several places where checks were needed to determine if the done stack was empty to report the desired error – this included the end of expression in comma assignment mode, comma in assignment mode, semicolon in assignment mode, and LET command with no variable after keyword.

One more check was required at the end of a statement (currently just end-of-line, but will be required for colon when that is implemented). If an EOL was received with the mode set to comma assignment (meaning more items in the list are expected – the mode is set to expression once an equal token is received), then an “expected equal or comma for in assignment” error is reported. A new end statement table entry flag was added for this.

The giant switch statement for the error messages in the test source file was not desirable. These eventually need to be placed elsewhere. Putting them in an array is the logical choice, but how to index the array? One way is to make sure the entries are in the same order as the token status enumeration, but this requires care to make sure it is correct and when it is not, the problem is difficult to debug. So a structure was added that contains the token status value and the string. During initialization, an index conversion array is set up, and during set up is validated to make sure there are none duplicated or missing – just like with the codes enumeration values in the table entries.

Since the error mechanism is almost identical to that used with table errors, instead of cloning this code (a common, but bad, practice of many programmers), an error template structure was implemented to be used for the token status message errors and table errors (the token status message errors only require the duplicate and missing error types). The routine to print the errors in the error list is also defined in the template in the include file. Putting calls to the fprintf() standard library function in this function is a bad idea, so a pointer to generic print function is passed to the error reporting template function. For now the print function passed just outputs to the standard error stream.