Command Centric Translator

The core of the current translator design has tokens fed to it one by one and is uses various states and modes to determine what type of tokens are expected and how they should be processed.  This design is rather complex and will make the implementation of more complex commands (like IF-THEN-ELSE and FOR-TO-STEP) very difficult.

The new translator design will be command centric.  What this means is that instead of handling each token individually from the bottom, the commands themselves will determine how their particular syntax will be translated.  The translator will start by reading a token, determining the command, and then calling the command specific translation routine.

There will be several routines to support getting the parts of commands these command translation routines will use including getting an expression, getting a variable reference, getting a constant, and getting a command.  Each of these functions exit once a token is reached that it does not handle and return that token.  For example, a semicolon would terminate an expression routine and return the semicolon token.  The caller would then decided how the semicolon will be handled (like in a PRINT statement), or if it is an error for the command (like in an IF-THEN statement).

For example, for an assignment statement, the LET translation routine first gets a variable reference, checks the returning token for a comma or equal operator, if a comma then will repeat getting a variable reference, else it would finish up by getting an expression.  An error would be reported at any step that is not valid (or if say the types don't agree).  Upon a successful command syntax, the token terminating the expression would be returned by the LET translation routine to the caller.

Each command translation routine would call the appropriate support routines for getting the various parts of the command's syntax and will return either an error or the token terminating the command.  The main line translator would expect either a colon (in which case it would look for another command), or an end-of-line token.  For an IF-THEN, after receiving the THEN token, would also call the get command routine, but in addition to looking for a colon or an end-of-line, would also look for an ELSE or ENDIF token.