HP 3000 Manuals HP 3000 Manuals
Operand Lookup Precedence
When expressions are scanned and parsed, they are ultimately broken down
into a series of tokens, which represent either operators or operands.
The preceding sections of this chapter introduced all the possibilities
for operand tokens in expressions, thereby answering the question, "What
sorts of things can be used as operands?" This section deals with the
converse: "Given an operand, what sort of thing is it?"
The process of evaluating an operand token can be modeled by a list of
possible interpretations of a token. The unknown token is tested against
each of the possibilities in the list, in the specified order, with the
first match determining the token's meaning.
The following list determines the interpretation of an operand token:
1. Test for a string literal or a numeric literal in the current
input base.
2. Test for a predefined variable.
3. Test for a user-defined variable.
4. Test for a predefined function.
5. Test for a macro.
6. Test for a procedure name symbol in the current mode, subject to
the search path in effect.
7. If still unresolved, fail.
There are two operand modifiers that, when prefixed to an operand, alter
the above search order for that operand. The exclamation point (!)
signals that the operand to which it is prefixed is not to be treated as
a numeric literal. This prevents the token from being mistaken as a hex
constant and initiates the operand search at step 2.
A question mark prefix (?) indicates that the operand is to be treated
as a procedure name symbol and that the entry point or export stub
address of the named procedure is being referenced instead of its
starting address. The search for such symbols begins with step 6.