Translator – Sub-String Debugging

To implement the sub-string change, not pushing the sub-string function to the done stack leaving its string operand on the stack (to carry to the next token), is accomplished by using the same mechanism that prevents print function from being pushed on the done stack (set the done push flag to false). With the number of operands being left set to zero, the sub-string function's string operand will be left on the done stack.

As debugging continued, nothing was getting attached to some AssignStr tokens. The assign command handler was only attaching tokens of the String data type, not the TmpStr data type returned (by the concatenate operator and the non-sub-string functions). In these cases, the AssignStr code will be changed to the AssignStrTmp code, but none of the associated codes for TmpStr arguments have been implemented yet (that will come next). Therefore, this will be left as is for now (TmpStr tokens will not be attached to AssignStr).

The new sub-string implementation (not pushing them on the done stack), made sub-string assignments stop working (produced “done stack empty” errors). The variable being assigned was popped from the done stack because it was not needed since it doesn't need to be attached to a token. When the assignment operator (equal) went to look for what was being assigned to determine which assignment code was needed, the done stack was empty. In this case, the sub-string function needs to be on the done stack. Therefore, a check was added to still push the sub-string function token if its reference flag is set.

The sub-string change also affected error reporting - the “expected numeric expression” error for a statement like Z=B+MID$(A$,2,3) was now incorrectly pointing to the A$ instead of the MID$ token (because the A$ carried forward and the MID$ token was not on top of the done stack).

To correct this problem, the code at the end of the find code routine that returns the appropriate error when an operand of the wrong data type was modified. If the last token appended to the output list doesn't match the top token on the done stack and the last token is a sub-string function, then the token returned is set to the sub-string token instead of the top token.