Short Functions

Kam Kasravi kamkasravi at yahoo.com
Mon May 23 14:55:28 PDT 2011


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.
They also are a good fit for transpilers though I realize this is not a TC39 goal.


________________________________
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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