New Translator – User Functions

User functions can take two forms, a full user function (using the FUNCTION syntax) or a simple define function (using the DEF FN syntax).  A full user function will pass arguments by reference.  This only applies to variables and array elements.  Results of expressions will be passed by value.  To keep things consistent internally, a temporary value will be allocated and a pointer to it will be passed, so all arguments will be a reference.  To force a single variable or array element to be passed by value, it can be surrounded by a set of parentheses.

Define functions will have two forms, a single line form that looks like an assignment and a multiple line form (that will end with an END DEF statement have one or more assignments for the return value).  Unlike full user functions, arguments to define functions will only be passed by value.  This make sense for the single line form since the arguments can't be assigned inside the function, and to keep the internal code consistent between the two forms, the multiple line form will also have arguments passed by value.  Arguments will be local variables, so any assignments will not affect the original variables.

This is the same method of argument passing used by QBASIC, and seems to be a reasonable design choice, so will also be used for this project.  Subroutines (the SUB syntax) will use the same pass by reference scheme as full user functions.  The passing of entire arrays will be dealt with later.  QBASIC allows this by listing the array name followed by an opening and closing parentheses with no subscripts.  This same syntax may be used for this project.

To handle function calls in the translator, the reference flag of an operand is set if it is an identifier with or without parentheses.  These tokens could end up being function calls, but this will be handled by the encoder.  Identifiers with parentheses could also end up being an array, where its arguments are integer subscripts.  Again this will be handled by the encoder, which will add any needed internal convert to integer codes (for double subscripts) or report errors for string subscripts.  The reference flag in any subscripts will be ignored.  Regardless of whether the identifier is an array or function, the translator will attach a pointer to each argument for the encoder.