Execution – INPUT command

To prove that the selected translation is appropriate, consider what occurs during execution, here are some example INPUT statements along with their translations:

INPUT A  InputGet'Question' A<ref> InputDbl Input
INPUT "How many: ",A%  "How many: " InputGet'Prompt' A%<ref> InputInt Input
INPUT P$+C$,A$;  P$ C$ +$ Input'Prompt' A$<ref> InputStr Input'Tmp+Keep'
INPUT,A,B%  InputGet A<ref> InputDbl B%<ref> InputInt Input

If there is a prompt string expression, its result will be on top of the evaluation stack. At the InputGet code, if the Prompt sub-code flag is set, then the string on top of the stack is output. If the Question sub-code flag is set, then a “? ” is output. The location of the InputGet code is pushed to the stack (to be used if an error occurs so that the InputGet can be returned to). The characters are input into a buffer until an Enter key terminates the input. There will be a status flag variable to keep parsing status of the input (initialized to None) and a value counter variable to count the number of input values (initialized to zero).

A variable reference is pushed to the evaluation stack. At an InputType code, the status flag is checked for a None or a Comma status, otherwise an error has occurred. The input buffer is scanned for a value token. If the value is the correct type, or can be converted to the correct type, then it is pushed to the stack, otherwise an error occurs. Finally, a pointer to an assign code run-time function for the data type is pushed to the stack.

At the Input code, the status flag is checked to make sure that it is set to EOL (a Comma status indicates there is more input, which is an error). An assign function pointer is popped from the evaluation stack and then called, which assigns the value to the variable that is the stack (both are popped by the assignment). This repeats for each value until the input value counter is decremented to zero. The InputGet code location is popped from the stack and finally the prompt string is popped from the stack. If the TmpStr sub-code flag is set, then the temporary prompt string is deleted. If the Keep sub-code flag is not set, the Print function is called to advance to the next line.  Next, some more execution details...