Hi everyone,
I am confronted with an implementation choice that I expect to be not so
rare, and I wonder what "the Pharo way" is for dealing with it. I will
use a toy example for illustration, my real case is more complex but not
fundamentally different.
Suppose I want to represent arithmetic expressions that support various
operations (evaluation, simplification, compilation to whatever
language, ...). In the textbook discussion, I'd have a class hierarchy
such as
Expression (abstract)
IntegerExpression
VariableNameExpression
SumExpression
ProductExpression
...
What I really want is not some IntegerExpression, but plain Pharo
integers, and for variable names I want to use plain Pharo symbols.
>From my current understanding of Pharo, my options are
1. Use wrapper objects for integers and symbols, i.e. have a class
IntegerExpression that stores an integer in an instance variable.
2. Add the methods of my abstract Expression class to all the classes
representing integers and symbols.
3. Implement my own dispatch that does not rely on method lookup.
None of these really looks attractive. 1) adds a lot of overhead, both
in the code ("IntegerExpression withValue: 5" rather than just "5") and
at runtime. 3) also adds a lot of overhead because I have to implement
my own dispatch. 2) would probably be the least effort, but looks like a
kludge.
For comparison, in the Lisp world (CLOS, Racket, ...) that I know much
better, I would use generic functions and provide implementations for
integers and symbols as well as for my own Expression types.
So... how would you approach this problem?
Thanks in advance,
Konrad.
