Walter Bright pisze:
aarti_pl wrote:
I know that quite a few people here doesn't like to allow users to
define their own operators, because it might obfuscate code. But it
doesn't have to be like this. Someone here already mentioned here that
it is not real problem for programs in C++. Good libraries don't abuse
this functionality.
The problem with user defined operators is:
1. User defined tokens - mixes up lexing with semantic analysis
2. User defined syntax - mixes up parsing with semantic analysis
and then we're in C++ land :-(
"retard" probably already answered it.
I was thinking about something like below:
symbols = '!...@#$%^&*' //quick & dirty definition
identifier = '[a-zA-Z][a-zA-Z0-9]*' //quick & dirty definition
Prefix operator:
1. [symbols][whitespace][identifier]
2. [identifier]whitespace[identifier]
Postfix operator:
1. [identifier][whitespace][symbols]
2. [identifier]whitespace[identifier]
Infix operator:
1. [identifier][whitespace][symbols][whitespace][identifier]
2. [identifier]whitespace[identifier]whitespace[identifier]
With precedence defined as above: first prefix, then postfix, then infix.
Should work...
Unless such have a unique grammar that can be lexed and parsed:
a :string: b
where string is the user defined name, so you can do things like:
a :^^: b
and define your own pow operator. The problem with this approach is the
sheer ugliness of it.
This might be also acceptable. Especially with `` syntax. (I know it's
currently for strings).
----
I believe that user defined operators will have positive impact on D
language. Please notice that always when you have more power, then you
can make more bad things. But you can also do more good things! And
doing good things or doing bad things is not something what should
programming language care of. Programming language is IMHO just for
giving good tools. User should decide how to use them.
I think there aren't enough good reasons to introduce new syntax if it
will not allow user defined operators. It will be rather source of
confusion if we only allow to pass few symbols as strings: strings are
about 'freedom' of content. So using it for passing just a few symbols
is for me "corner case".
BR
Marcin Kuszczak
(aarti_pl)
