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Comment by JoeAltmaier | Hacker News Reader

Another way to express this is, I'd like a language keyword for "left hand side of assignment". Then for x=x+1 I could say

     x = <LHS> + 1;

It could then get arbitrarily complex. E.g.

     x =  (<LHS> + 1) / atan(<LHS>) - <LHS>;

and no matter how complex 'x' was in practice, the compiler (and the code reader) could keep track of what was happening.

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Is there a significant benefit to this over using a new name for the result?

    y = (x + 1) / atan(x) - x;
    x = y; // If you're in a loop and updating some value

If would hope/imagine that a compiler could reduce the two to the same code - and I don't think it reads any worse. Is there a downside beyond the extra line of code?

To be clear: the assignment isn't the optimization; its the use of a symbol for 'x' on the rhs so that the compiler can recognize it. To illustrate that

    X &x = { complex reference expression for x }
    y = (x + 1) / atan(x) - x;

Now the compiler has the clues it needs to write good code. And with language support I don't have to introduce new names for each occurrence; just one name like <LHS> that readers can quickly learn.

> And with language support I don't have to introduce new names for each occurrence;

Having <LHS> as a name is only useful I think if you don't want to give it another name? I was asking what's the downside of giving it a name.

Name proliferation is a famous issue. One-use names are evil.

why ? Could you elaborate ?

Because from my point of view, it could be only the case only if the scopes are weak or underused, or names are bad (too short, ect). After SSA is all about one-use names.

I disagree. Names are comments. You don't want more mutable state across large scopes, but using intermediate names can help comprehension.

I think I get what you mean, but I cannot imagine a single example where your proposed <LHS> keyword would be a good solution: IMHO, if I need a keyword to make the RHS understandable to the reader and the (much smarter) compiler, a macro or function is called for to encapsulate the RHS in a named and documented unit of code.

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