Brown suggests that the internal language be in the form of RPN (Reverse Polish Notation) and I agree. As it will allow the program to be easily and quickly run. Basically the following commands:
A = B + C * 4
PRINT A+B;TAB(20);C+5
Would be translated to RPN, which would symbolically be represented as something like:
A B C 4 * + =(assignment)
A B + 20 TAB C 5 + PRINT
When the program is run, each operand is pushed onto a stack. When an operator is reached, it's operands (e.g. two for *, one for TAB, etc.) are pulled from the stack, the operation is performed and the result is pushed back onto the stack. When a command is reached (e.g. PRINT), it preforms it's procedure on the values that are currently on the stack. It's more involved than this, but this is the general idea. The actual internal language is encoded from the symbolic RPN representation.
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