Allen's lambda syntax proposal

Maciej Stachowiak mjs at
Mon Dec 1 12:59:03 PST 2008

On Nov 29, 2008, at 10:30 PM, Brendan Eich wrote:

> At the TC39 meeting two weeks ago in Kona, we had a brief  
> bikeshedding discussion about lambda syntax and why it matters.  
> Observation: blocks in Smalltalk being lightweight means users don't  
> mind writing them for control abstractions, compared to JS functions  
> in ES3. In Smalltalk, ignoring JS, it's hard to beat [ and ] as  
> overhead, although one must count the message selector and its  
> punctuation too.
> Allen Wirfs-Brock put his proposal, which will not shock you who  
> know Smalltalk or Allen, on the whiteboard:
> // Instead of lambda (a, b, c) { ... }, why not:
> { |a, b, c| ... } ?

I like the brevity, but having the formals inside the block and in ||  
delimiters seems like it will look weird in an ECMAScript program. For  
function declarations the parameters go in parentheses, and for calls  
(presumably also for lambda calls), the arguments go in parens. If  
brevity is important, why not lift the lambda syntax from modern pure  
functional languages:

\(a, b, c) { ... }

That's backslash as a lambda operator. This has one more character  
than your version, but will make formals and parameters look the same  
for functions, lambdas, and calls, and will avoid putting the formals  
inside the body which I think is confusing and visually hard to scan.


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