To be fair, after a long reflection, I have been concluding that no other
proposal beat {|| ...} for block lambda at this time. Also, I’ve found some use
cases where block-lambda are actually useful (something I was really curious
about before thinking about it). In the future, they may even be used a lot by
transpilers to emulate new language constructs in a ES-friendly way.
The main point I dislike with the current proposal is that it makes
block-lambda used at places where I think they should not. It’s not because
they are useful to solve some problems they are useful to fix all. Most of the
time, when we want a lambda, we don’t want TCP. We want a new function. Just
and only that. Since we want a new function, we are requesting function-like
semantics. It’s logical.
An exemple:
function A() {
let ret = {|x| return x; };
let inc = {|x| x+1 };
let j = 0;
while (true) {
if (j > 3) ret(j);
j = inc(j);
}
}
I don’t think “inc” should be a block-lambda. It can be, if someone do that, I
would not bother modifying the code. But it’s not the natural way to think.
What we need here is not an “extension” of the current function (which is a
block lambda is), we need a new function.
The problem is that the current syntax is too long :
let inc = function(x) { return x+1; }
I think (but I don’t say it’s what should be done, it’s up to debate) that
alongside block-lambda, we should introduce a ‘canonical’ lambda proposal, that
would just be syntaxic sugar for plain old functions.
The syntax I propose would be:
‘@(‘ + <argument-list> + ‘)’ + <statement>;
// or if too complex
‘@(‘ + <argument-list> + ‘)’ + ‘{‘ + <statement> + ‘}’;
That would desugar to:
(function lambda_lineX_colY_fileZ(<argument-list>) {
return do {
<statement>
};
}).bind(this);
That would allow the following samples :
let inc = @(x) x+1;
array.map(@(x) x+1);
array.map(@(x) {
if(x.hasKey(‘a’)) {
x.get(‘a’)
} else {
undefined
}
});
and the more complex ones :
array.map(@(x) {
while(x.parentNode) {
x=x.parentNode;
if(x.tagName==’DIV’) { return x; }
}
console.log(‘An element that has no parent DIV has been found.’);
return undefined;
});
Please note that the last one seems very complex to write using a block-lambda :
array.map({|x| let returnValue;
while(x.parentNode) {
x=x.parentNode;
if(x.tagName==’DIV’) { returnValue=x; break; }
}
if(returnValue) {
returnValue;
} else {
console.log(‘An element that has no parent DIV has been found.’);
undefined;
}
});
That proposal does offer some middle ground between
- ‘functions’ (classical functions)
- ‘lambdas’ which are local functions that are not meant to go outside the
scope of an action
- ‘block-lambdas’ which are internal functions that are not meant to go outside
the scope of a function scope.
Anyone can use what’s the most convenient for him, I think there’s room for all
those things.
François
From: Axel Rauschmayer
Sent: Wednesday, January 18, 2012 8:48 PM
To: Oliver Hunt
Cc: Brendan Eich ; es-discuss Steen
Subject: Re: Block lambda is cool, its syntax isn't
Maybe the problem here is that I don't like the block-lambda concept itself.
I’m curious: What do you dislike?
--
Dr. Axel Rauschmayer
[email protected]
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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