Short Functions

Kam Kasravi kamkasravi at yahoo.com
Mon May 23 16:38:07 PDT 2011



On May 23, 2011, at 4:08 PM, Brendan Eich <brendan at mozilla.com> wrote:

> On May 23, 2011, at 2:55 PM, Kam Kasravi wrote:
> 
>> I've been experimenting with PEG/packrat parsers and how well they do on the ecmascript grammar.
>> Since these do not use lexers and are LL(n) they may be a better fit.
>> There are a few implementations out there written in JS - ometa and pegjs come to mind.
> 
> Mark and Tom used Ometa for http://code.google.com/p/es-lab/ -- slo-o-o-o-wwwww.

Yeah it has no memoization. Pretty cool nevertheless as far as what he was able to do. Though I really like what Dave is doing on narcissus.
> 
> 
>> They also are a good fit for transpilers though I realize this is not a TC39 goal.
> 
> We need to consider browser implementations, which must lex and parse quickly, and which all (AFAIK) use hand-written lexers and parsers.
> 
> /be
> 
>> 
>> From: Waldemar Horwat <waldemar at google.com>
>> To: Brendan Eich <brendan at mozilla.com>
>> Cc: es-discuss <es-discuss at mozilla.org>
>> Sent: Monday, May 23, 2011 2:09 PM
>> Subject: Re: Short Functions
>> 
>> On 05/21/11 23:53, Brendan Eich wrote:
>> > That's accurate. But I discounted arrow functions because to be usable, to have the syntax you show above, requires GLR parsing (if bottom up; top-down may be easier, haven't proven it yet).
>> 
>> GLR parsing would be wild in ECMAScript due to the fact that the lexer is dependent on the parser's current state.  A GLR parser is working on a quantum superposition of multiple states in parallel, so if it encounters a / then some of the superposed states may direct the lexer to interpret it as a division symbol while others direct it to start scanning a regular expression.  So now you need a quantum entanglement of lexers corresponding to the superposed parser states the GLR parser is considering.  Semicolon insertion would also be be forced into quantum entanglement with the superposed parser states.
>> 
>> Do we really want to go there?
>> 
>>     Waldemar
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