declarative style evaluation.js

declarative style evaluation.js

/*
  Declarative style evaluation.
  Advantages
    order of evaluation is not important
    evaluation is lazy i.e. its evaluated only if required
    auto memorization of evaluation (only for pure fns)
    expressions are writed as in math, no mutable values
*/

Object.prototype._let = #(name, _calc) {
  fix self = @
  @__defineGetter__(name, #{
    var ret = _calc()
    delete @[name] // memo result
    @[name] = ret
    -> ret
  })
}

fix _solveQuadraticEquation = #(a, b, c) {
  with({})
  {
    _let('D', #{ -> b*b - 4*a*c })
    _let('x1', #{ -> (-b + Math.sqrt(D)) / (2*a) })
    _let('x2', #{ -> (-b - Math.sqrt(D)) / (2*a) })
    
    if(D < 0)
      -> []
    else if(D == 0)
      -> [x1]
    else
      -> [x1, x2]
  }
}

_log(_solveQuadraticEquation(1, 0, -1))