Targeting the ecmascript AST

kevin curtis kevinc1846 at googlemail.com
Tue Mar 24 09:24:17 PDT 2009


Following on from the recent discussions on ecmascript as a compiler target
and Brendan's point re targeting the AST, I have coded a user-friendly
pseudocode-ish syntax which targets the V8 ecmascript AST: 'zedscript'
aka 'zed is ecmascript for dummies'. (And given the focus of the list
i won't be posting followup's - but i hope it may be of interest to some
readers).
The code can be found at:
http://code.google.com/p/zedscript/

Zedscript runs _in_ the V8 ecmascript engine. That is, there is no
parsing zedscript source -> javascript source phase. It targets the
AST directly.

The V8 scanning/parsing source code has been altered to allow the V8
engine to compile and run both ecmascript and zedscript. It reuses the V8
tokens/scanning/parsing/runtime/errorhandling machinery. This reduces
abstraction leakages and aids debugging. zedscript can call ecmascript
and vice-versa. (Calling jsfunction.toString() can be surprising however!).

A zedscript script can be run via the V8 shell:
./shell <zedscriptfile>

So, zedscript provides a thin layer of syntax sugar over the core
ecmascript semantics which will (hopefully):

    * show the emerging rich 3.1 and 4(Harmony) semantics in the best
      possible best light.
    * minimizes quirks and gotchas.
    * emphasize simplify, security, safety and speed. For instance
      ecmascript 3.1 'strict mode' could be enabled by default.
    * is not a port of existing languages e.g python, ruby. (Imho
      emcascript does not need 1001IronXXX ports.
      It needs one good alternate syntax - which can take inspiration
      from the sugar/syntax of other pragmatic languages - but can be
      considered a dialect of the core ecmascript semantics rather than
      a new language or port).
    * hits the sweet spot between succinctness and pseudocode readability.

The goal is to track ecmascript 3.1 and 4/Harmony and deliver
zedscript 3.1 and 4 on the V8 engine. (And maybe on tracemonkey and
sfx/nitro).  It could be considered a synthesis of Brendan's goal of sugar
for es4 and Douglas Crockford's idea re a 'new' language. I feel that some
users - especially those without a comp. sci background - will never get on
with the curlies syntax. An alternate syntax in addition to the
javascript syntax
- especially for esHarmony - could really help promote ecmascript as a general
purpose scripting language. Even if something like this never gets into the
browser it would be useful for server and desktop development.

Here an example 'ztest/sample.js'. Note how the script begins with
//zed to signal to V8 it's a zedscript file.
(This is a temporary solution).

//zed
// - currently has a dylan/moo -ish syntax
// - the parens around the expression could change to
//   a more ruby/lua -ish syntax, with optional do/then.

print("*** start\n")

var x = 10
var y = 20


// if has elif clauses
// and/or are aliases for &&/||
if (x == -99)
    print("FAIL")
elif (x == 10 and y > 15)
    print("OK")
elif (x == -99 or y > -99)
    print("FAIL")
else
    print("FAIL")
end


// not as alias for !
var b = false;
print(!b)
print(not b)

// fn as alias for function
fn times2(i)
    return i * 2
end

var z = 1
while (z <= 5)
    print(z + " : " + times2(z++))
end

print("\n*** end ");

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