34. Rewriting Expressions - Solution

In this exercise we ask you to rewrite some expressions or to understand the different forms that a solution can take. Some of the expressions are explained in https://medium.com/concerning-pharo/elegant-pharo-code-bb590f0856d0

34.0.1. Exercise: Examine the block expressions

	| sum |
	sum := 0.
	#(21 23 53 66 87) do: [:item | sum := sum + item].
	sum
34.0.1.1. Exercise:
  • What is the final result of sum?

Solution. The sum of all the numbers of the array: 250

34.0.1.2. Exercise:
  • Rewrite this piece of code to use explicit array indexing (with the message at:) to access the array elements. Test your version.

Solution. 

	| array sum |
	array := #(21 23 53 66 87).
	sum := 0.
	1 to: array size do: [ :i | sum := sum + array at: i ].
	sum
34.0.1.3. Exercise:
  • Rewrite this code using inject:into: (check the implementation of inject:into: and its users in the system to understand how to use it).

Solution. 

#(21 23 53 66 87) inject: 0 into: [:item :sum | sum + item]

34.0.2. Exercise: Comparing expressions

You can express in different way the same computation. Have a look at each of them and check the messages that you do not know. Look for their implementation. 

| array |
array := #(2 4 4 4 5 5 7 9).
((array - array average) squared sum / (array size - 1)) sqrt 
[ :input | ((input - input average) squared sum / (input size - 1)) sqrt ] 
    value: #(2 4 4 4 5 5 7 9) 
#(2 4 4 4 5 5 7 9) in: [ :input |
    ((input - input average) squared sum / (input size - 1)) sqrt ]
#(2 4 4 4 5 5 7 9) stddev