Issue 15367: OCL 2.2 Add endlet to make grammar extensible (ocl2-rtf)
Source: Model Driven Solutions (Dr. Edward Willink, ed(at)willink.me.uk)
Nature: Uncategorized Issue
Severity: 
Summary: Further to Bran Selic's observation on Issue 15357 that UML-specifics should not really impact the OCL core. This is easy for State via a ModelLiteralExp, but hard for Message which has associated concrete syntax.


The expression grammar could be made extensible to accommodate custom/orthogonal infix, prefix, suffix, precedence if an expression could be parsed by the generic:


expr ::= affixed (infix affixed)*
affixed ::= prefix* suffixed
suffixed ::= atom (suffix | '(' expr ')' | '[' expr ']' | '{' expr '}' )*
atom ::= '(' expr ')'
    | name
    | 'if' expr 'then' expr 'else' expr 'endif'
    | 'let' expr 'in' expr 'endlet'


The major problem is the missing 'endlet', which makes accurate parsing difficult and complex expressions easy for humans to misinterpret too.


Suggest introduce the 'endlet' keyword.
Resolution: 
Revised Text: 
Actions taken:
July 9, 2010: received issue
Discussion: 

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Date: Fri, 09 Jul 2010 06:59:47 +0100
From: Ed Willink <ed@willink.me.uk>
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To: issues@omg.org
Subject: OCL 2.2 Add endlet to make grammar extensible


Hi


Further to Bran Selic's observation on Issue 15357 that UML-specifics should not really impact the OCL core. This is easy for State via a ModelLiteralExp, but hard for Message which has associated concrete syntax.


The expression grammar could be made extensible to accommodate custom/orthogonal infix, prefix, suffix, precedence if an expression could be parsed by the generic:


expr ::= affixed (infix affixed)*
affixed ::= prefix* suffixed
suffixed ::= atom (suffix | '(' expr ')' | '[' expr ']' | '{' expr '}' )*
atom ::= '(' expr ')'
    | name
    | 'if' expr 'then' expr 'else' expr 'endif'
    | 'let' expr 'in' expr 'endlet'


The major problem is the missing 'endlet', which makes accurate parsing difficult and complex expressions easy for humans to misinterpret too.


Suggest introduce the 'endlet' keyword.


    Regards


        Ed Willink