Re: Expressions in ET ...

Bernd Schoeller wrote:
> Hello,
> 
> I am currently having a look at expressions generated by the Eiffel
> parsing tools (creating a processor for inferring the type for a given
> expression). For now I am stuck with a number of open cases.
> 
> Could somebody (Eric?) give an example of expressions that are of the
> following type:
> 
> ET_BRACKET_SYMBOL
> ET_PREFIX_FREE_NAME
> ET_PREFIX_NAME
> ET_ALIAS_FREE_NAME
> ET_ALIAS_NAME

I guess that all these are descendants of ET_EXPRESSION because
they are descendants fo ET_CALL_NAME which itself inherits from
ET_EXPRESSION. It would probably be better to make each descendant
of ET_CALL_NAME inherit (or not) from ET_EXPRESSION. I don't
remember why I didn't do it that way. Perhaps laziness or lack
of vision.

To my defense it should be noted that at some point it was invisioned
to allow code like this:

    a.infix "+" (b)

as an alternative for:

    a + b

Therefore the following:

    prefix "-"

would have been an expression, unless we would have required the usage
of Current:

    Current.prefix "-"

What is more questionable is that ET_OPERATOR, being an heir of
ET_CALL_NAME, is also a descendant of ET_EXPRESSION.

> ET_INFIX_CAST_EXPRESSION

If I remember correctly, with ECMA if we have something like that:

    5 + 4.0

the target is implicitly converted to the type of the argument.
Something like that:

    {REAL_64} [5] + 4.0

The new (converted) target is represented in the AST by an object
of type ET_INFIX_CAST_EXPRESSION.

> Also, I would like to know why ET_STATIC_CALL_EXPRESSION inherits from
> ET_CHOICE_CONSTANT.

I think that ISE allows code of the form:

    inspect foo
    when {WEL_CONSTANTS}.Some_constant then
         ...

-- 
Eric Bezault
mailto:ericb-D6Qt/9opevxWk0Htik3J/[email protected]
http://www.gobosoft.com



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