How to resolve the algorithm Accumulator factory step by step in the FreeBASIC programming language

Published on 12 May 2024 09:40 PM
#Freebasic

How to resolve the algorithm Accumulator factory step by step in the FreeBASIC programming language

Table of Contents

Problem Statement

A problem posed by Paul Graham is that of creating a function that takes a single (numeric) argument and which returns another function that is an accumulator. The returned accumulator function in turn also takes a single numeric argument, and returns the sum of all the numeric values passed in so far to that accumulator (including the initial value passed when the accumulator was created).

The detailed rules are at http://paulgraham.com/accgensub.html and are reproduced here for simplicity (with additions in small italic text).

Create a function that implements the described rules.

It need not handle any special error cases not described above. The simplest way to implement the task as described is typically to use a closure, providing the language supports them. Where it is not possible to hold exactly to the constraints above, describe the deviations.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Accumulator factory step by step in the FreeBASIC programming language

Source code in the freebasic programming language

' FB 1.05.0 Win64

' uses overloaded methods to deal with the integer/float aspect (long and single are both 4 bytes)
Type Bar
  Public:
    Declare Constructor(As Long)
    Declare Constructor(As Single)   
    Declare Function g(As Long) As Long
    Declare Function g(As Single) As Single
  Private:
    As Single sum_   '' can't be altered by external code
End Type

Constructor Bar(i As Long)
  sum_ = i
End Constructor

Constructor Bar(s As Single)
  sum_ = s
End Constructor

Function Bar.g(i As Long) As Long
  sum_ += i
  Return sum_  '' would round down to a Long if non-integral Singles had been added previously
End Function

Function Bar.g(s As Single) As Single
  sum_ += s
  Return sum_  
End Function

Function foo Overload(i As Long) As Bar  '' returns a Bar object rather than a pointer to Bar.g
  Dim b As Bar = Bar(i)
  Return b
End Function 

Function foo Overload(s As Single) As Bar  '' overload of foo to deal with Single argument
  Dim b As Bar = Bar(s)
  Return b
End Function 

Dim x As Bar = foo(1)  '' assigns Bar object to x
x.g(5)  '' calls the Long overload of g on the Bar object
foo(3)  '' creates a separate Bar object which is unused
print x.g(2.3) '' calls the Single overload of g on the Bar object and should print 1 + 5 + 2.3 = 8.3

Print
Print "Press any key to quit"
Sleep

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