On 08/25/2015 09:38, Claude Pache wrote:
I think the following grammar could work.
Replace the current (ES2015) PostfixExpression production with:
```
IncrementExpression:
LeftHandSideExpression
LeftHandSideExpression [no LineTerminator here] ++
LeftHandSideExpression [no LineTerminator here] --
++ LeftHandSideExpression
-- LeftHandSideExpression
```
And define UnaryExpression as:
```
UnaryExpression:
IncrementExpression
delete UnaryExpression
void UnaryExpression
typeof UnaryExpression
++ UnaryExpression
+ UnaryExpression
-- UnaryExpression
- UnaryExpression
~ UnaryExpression
! UnaryExpression
IncrementExpression ** UnaryExpression
```
The above is not a valid grammar. For example, parsing ++x leads to a
reduce-reduce conflict, where the ++ can come from either a UnaryExpression or
an IncrementExpression.
where the following production (which exists only to avoid to confusingly
interpret, e.g., `++x++` as `+ +x++`):
That makes no sense. ++ is a lexical token. The lexer always greedily bites
off the largest token it can find, even if that leads to a parser error later.
The parser does not backtrack into the lexer to look for alternate lexings.
For example,
x +++++ y;
is a syntax error because it's greedily lexed as:
x ++ ++ + y;
The parser does not backtrack into the lexer to look for other possible lexings
such as:
x ++ + ++ y;
```
UnaryExpression:
++ UnaryExpression
-- UnaryExpression
```
yields a static SyntaxError (or a static ReferenceError if we want to be 100%
compatible ES2015).
This is a problem. It makes ++x into a static SyntaxError because x is a
UnaryExpression.
If you got rid of these two ++ and -- productions in UnaryExpression, that
would solve that problem (and I think make the grammar valid).
Waldemar
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