ResistorColors in Unison

ResistorColors.md

If you want to build something using a Raspberry Pi, you'll probably use resistors. For this exercise, you need to know two things about them:

• Each resistor has a resistance value.
• Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read. To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values. Each band has a position and a numeric value. For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.

In this exercise you are going to create a helpful program so that you don't have to remember the values of the bands. The program will take color names as input and output a two digit number, even if the input is more than two colors!

The band colors are encoded as follows:

• Black: 0
• Brown: 1
• Red: 2
• Orange: 3
• Yellow: 4
• Green: 5
• Blue: 6
• Violet: 7
• Grey: 8
• White: 9

From the example above: brown-green should return 15 brown-green-violet should return 15 too, ignoring the third color.

ResistorColors.u

use base.Nat.fromText

unique type Color = 
    Black
  | Brown
  | Red
  | Orange
  | Yellow
  | Green
  | Blue
  | Violet
  | Grey
  | White

getVal : Color -> Text
getVal c = match c with Color.Black -> "0"
                        Color.Brown -> "1"
                        Color.Red -> "2"
                        Color.Orange -> "3"
                        Color.Yellow -> "4"
                        Color.Green -> "5"
                        Color.Blue -> "6"
                        Color.Violet -> "7"
                        Color.Grey -> "8"
                        Color.White -> "9"

value : Color -> Color -> Nat
value a b = match .base.Nat.fromText (getVal a ++ getVal b) with  
  None -> 0
  Some x -> x

test> value.tests.ex1 = 
  check ( value Brown Black == 10)

test> value.tests.ex2 = 
  check ( value Blue Grey == 68)  

test> value.tests.ex3 = 
  check ( value Yellow Violet == 47)    

test> value.tests.ex4 = 
  check ( value Orange Orange == 33)