Re: Parenthesized Target Notation (was: Partial retraction)

Richard A. O'Keefe wrote:

> Concerning
> 	>	  require
> 	>	  h
> 	>	  (a + b).g
> 	>  
> 	>
> =?ISO-8859-1?Q?Val=E9ry_Croizier?= <[email protected]> wrote:
> 	The ambiguity remains because 'h' could be either a parameterless 
> 	feature or a feature that takes one argument.
> 
> Yes, avoiding the ambiguity means not shutting your eyes to everything
> you know.
> 
> There are other places in the new syntax where there are, um, awkwardnesses.
> Now that there are both 'bracket aliases' _and_ tuples, I invite you to
> consider the possible confusions.
> 
> 	Sure, it was a bit late to change one's mind ...
> 	
> Exactly so.
> 

Concerning semicolons: a semicolon in Eiffel is used to separate or terminate 
elements within certain lists. For example, a semicolon is used to separate or 
terminate instructions in a compound, index clauses in an indexing, assertion 
clauses in an assertion and declaration groups in a declaration list. A 
semicolon is often optional. An example that does illustrate a necessary, i.e. 
not optional, semicolon is:

Example 1)
    do
       x := y;
       (p + q).r

The use of barred parentheses (| ... |), under the new ECMA syntax, would render 
the semicolon above optional. The introduction of these new parentheses does 
appear aimed at establishing the following semicolon rule:

    A semicolon is optional

For current Eiffels the rule is:

    A semicolon is optional, except where it is not optional

This is not as silly as it sounds since it can be expanded to:

    if you remove a semicolon and the result is code that would be parsed to
    produce a different list of elements then the semicolon is not optional and,
    conversely, if you remove a semicolon and the result is not a different list
    of elements then the semicolon is optional

So a parser can decide whether a semicolon is optional or necessary.

The semicolon is a slippery customer: the following semicolon looks necessary 
but is in fact optional:

Example 2)
    do
       create x;
       (p + q).r

More importantly there are additional instances of necessary semicolons:

Example 3)
    ensure
       b;
       -m > n

And:

Example 4)
    ensure
       tag_only:;
       b

In the last example removing the semicolon results in a parse that identifies 
just one element rather than the original two.

For current Eiffels, here is an analogous example in indexing:

Example 5)
    indexing
       tag_only:;
       01, May, 2005

The semicolon necessity in examples 3) and 4) could be removed if the ECMA 
standard demanded that an assertion clause always has a tag - like the required 
note_name for a note_entry in the new notes (was indexing) construct. However, I 
do not know of a list of necessary semicolon instances that claims to be 
complete, perhaps there are more instances to be uncovered.

  - Ian Elliott