guarding your cases

Guarding Your Cases

Guard Example

Here is an example of a function that uses guards:

traffic :: String -> String
traffic light
    | light == "green" = "go!"
    | light == "red" = "stop!"
    | otherwise = "slow down."

The Problem

Today, we’ll be creating your own miniature program that allows you to play Rock-Paper-Scissors! To start off, here are the type you’ll need:

data Move = Paper | Rock | Scissors deriving (Eq, Show)
data Result = Win | Draw | Lose deriving (Eq, Show)

(The first part of the problem is writing a function which takes a move as input and finds the move which beats it). We have written most of the function but some parts are missing:

beats :: Move -> Move
beats move
    | move == Paper = _
    | __ == ___ = _
    | otherwise     = _

Now write a function which returns the result to a set of moves. Here is a framework:

score :: Move -> Move -> Result
score playerA playerB ...

The Case with Guards

Congratulations, you can now play playgroud rock-paper-scissors with your friends. However a challenger approaches, and they only trust cases. Try rewrite both beats and score with cases!

Challenge

The following table gives scores for people sitting next to each other. Given a list of the three people (as strings) calculate the score of the sitting arrangement:

	Jay	Edmund	Ranald
Jay	/	2	4
Edmund	2	/	-1
Ranald	4	-1	/

Use cases and guards!