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4 points by pg 5985 days ago | link | parent

I'm still uncertain what to do about this. One reason is that the two-variable case is much more common than all the rest put together. So if I could think of a very clean way to represent a fn of two vars, that might be better.


3 points by febeling 5985 days ago | link

This looks like the obvious next step:

[+ _ __]

But then you would have trouble denying this unreadable ugliness:

[+ _ __ ___ ____]

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6 points by ndanger 5985 days ago | link

What about combing it with nex3's idea?

[+ _1 _2 _3 ...]

_1 could be an alias for _

[+ _ _2]

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2 points by greatness 5984 days ago | link

I was thinking that _ would be merely _0, ie _1 would be the second argument. But at this point that's not really the question, the question is how will the interpreter know how many arguments the function takes?

Maybe something like:

  [[[+ _ _1 _2]]]
Could be shorthand for:

  (fn (_ _1 _2) (+ _ _1 _2))
But, then, what if you want to use square bracket notation inside of that? For example, what if you want to create a two paramater function that creates a one paramater function?

  (fn (x y) [+ x y _])
would be impossible. Unless you use currying or something on these special ones. Incidentally, a curry function:

  (def curry (f . args)
    (fn args2 (apply f (join args args2))))
Then you could simply do:

  (curry + var1 var2)
Assuming you already have the variables. For smarter currying it'll need to be done by the interpreter.

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1 point by are 5984 days ago | link

In this expression:

[+ _1 _2 _3]

... the interpreter already knows that _2 is the second anonymous parameter to the function literal, without parsing the "2" token.

So you could instead have:

[+ _ _ _]

... and specify the index only if you actually want to use the parameter outside of the function literal (and there, _ would still be shorthand for _1).

And BTW, this whole thing should work with rest parameters, so that in:

[+ _ . _]

... _2 will denote a list.

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1 point by robbie 5984 days ago | link

"... the interpreter already knows that _2 is the second anonymous parameter to the function literal, without parsing the "2" token."

it could be the third parameter.

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1 point by are 5984 days ago | link

We may be talking past each other.

I'm just saying that if you have several anonymous parameters in the parameter list of the function literal, it is just as well that you represent them with the same token _within the parameter list_. The parameter list is ordered, so the interpreter knows which is which anyway. If you then want to refer to one of the anonymous parameters _outside of the parameter list_, you use a token WITH an index, to identify the position of the particular anonymous parameter in the parameter list.

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1 point by Xichekolas 5984 days ago | link

I thought the whole point of the bracketed function literal syntax was that you don't have a parameter list...

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1 point by nex3 5985 days ago | link

I thought about suggesting this as one of the prefix characters, but underscores just don't feel very prefixy.

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1 point by Xichekolas 5984 days ago | link

One thing about underscores is that they kind of stand out... but I agree, they are a bit weird. Other options could be (@, $, %, *, ?)

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1 point by chl 5984 days ago | link

In K, {x+y+z} equals {[a;b;c]a+b+c}.

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