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Comment by c3534l | Hacker News Reader

I've always liked the idea of a language that combined syntax level support for functional reactive programming and symbolic programming. So you define z as x + y. Then you change the value of x and that change cascades across your program, like a spreadsheet almost.

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Try Mozart/Oz [1]. For example, a symbolic constraint solver for Minesweeper [2] had been written in it.

[1] https://mozart.github.io/

[2] https://www.info.ucl.ac.be/~pvr/minesweeper.pdf

k/q does this. They're called views[1]

    z::x+y
    x:42
    y:42
    z
    y:69
    z

[1]: https://code.kx.com/v2/ref/view/

And JS :-).

   let x = ()=>42
   let y = ()=>42
   let z = ()=>x()+y()
   z() // 84
   y = ()->69
   z() // 111

Not exactly the same thing, for one these aren't function calls, and for another the view is memoized: You can see the difference with some print statements:

    q)z::show(x;y;x+y);x+y
    q)x:42
    q)y:42
    q)z
    42 42 84
    84
    q)x:69
    q)z
    69 42 111
    111
    q)z
    111

Views are also aware of what's changed:

    q)a:1234
    q)z
    111
    q)y:69
    q)z
    69 69 138
    138

Well, you can do that in any language with first-class functions. But there's obviously a syntactical difference between a function invocation and a variable read.

Isn't that Haskell? Or any other declarative, lazily-evaluated landuage.

Granted, you need to use something like the ST monad to be able to "change the value of x," but once you do, all other values fall into place like dominoes.

That's pull rather than push, though.

I understand that is how object oriented databases work. For example, you can define the equation for a financial derivative, then change the price of one of the components and derivative price is updated automatically.

You can do this easily in lispy languages with eval

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