SICP 1.7 Solution

1.7-improving-sqrt.scm

(define (good-enough? guess next-guess)
  (< (/ (abs (- guess next-guess)) guess) 0.001))

(define (average x y)
  (/ (+ x y) 2))

(define (improve guess x)
  (average guess (/ x guess)))

(define (sqrt-iter guess x)
  (if (good-enough? guess (improve guess x))
      guess
      (sqrt-iter (improve guess x)
                 x)))

1.7-improving-sqrt.vb

' Just for kicks
Function Average(X As Double, Y As Double) As Double
    Average = (X + Y) / 2
End Function

Function Improve(Guess As Double, NextGuess As Double) As Double
    Improve = Average(Guess, X / Guess)
End Function

Function IsGoodEnough(Guess As Double, NextGuess As Double) As Boolean
    IsGoodEnough = (Abs(Guess - NextGuess) / Guess) < 0.001
End Function

Function SqrtIter(Guess As Double, X As Double) As Double
    If (IsGoodEnough(Guess, Improve(Guess, X))) Then
        SqrtIter = Guess
    Else
        SqrtIter = SqrtIter(Improve(Guess, X), X)
    End If
End Function