Hi!

I was trying to understand the Self grammar to implement a Self parser. I failed. Now I've a couple of questions regarding the ambiguities of the grammar. I'm working with the grammar shown in appendix 2.C of the Self 4.0 language reference.

Currently, I've two problems: a) How can I distinguish a simple expression enclosed in parenthesis from an object definition - and b) how to detect the end of a slot list?

I expanded the BNF rules to deal with message precedence as follows:

expression = keyword-message keyword-message = binary-message {keyword-send} | resend... keyword-send = small-keyword keyword-message {cap-keyword keyword-message} binary-message = unary-message {binary-send} | resend... binary-send = operator unary-message unary-message = primary {unary-send} | resend... unary-send = identifier primary = [receiver] receiver = identifier | constant

now, to allow expressions in parentheses, we need to add a rule

receiver = "(" expression ")"

however, now there's no chance to distinguish this from the regular-object definition, which is one alternative of constant, because "( 1 + 2 )" could also be a valid method object. Did I miss something here?

The second problem is with operators. Appendix 2.B says about operators:

op-char = ... '-' | '^' | '|' | ... operator = op-char {op-char}

which especially means that ^ and | are valid operators and furthermore, that for example '=-1' is ambigious. Let's ignore _that_ problem for now. My trouble are ^ and | as operators.

Currently, my parser will fail on (| a = 1 |) because it thinks that there's a slot "a" to which a binary expression is assigned of which the second part is missing. It doesn't detect the end of the slot list.

My parser also fails on this, which might be a legal Self expression according to the grammar: (| | x = ( ... ) |) If "|" is a valid operator, it must be possible to use it in a binary-slot definition.

Here's another problem with '^': ^12 can be parsed both as "self ^ 12" and "return 12".

My solution would be to bann ^ and | as valid operators, but what does the Self spec say, what does the offical Self parser do? I need help.

Thanks in advance, bye -- Stefan Matthias Aust // Are you ready to discover the twilight zone?

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