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# craigmaloney's solution

## to Grains in the Scheme Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.

There once was a wise servant who saved the life of a prince. The king promised to pay whatever the servant could dream up. Knowing that the king loved chess, the servant told the king he would like to have grains of wheat. One grain on the first square of a chess board. Two grains on the next. Four on the third, and so on.

There are 64 squares on a chessboard.

Write code that shows:

• how many grains were on each square, and
• the total number of grains

## For bonus points

Did you get the tests passing and the code clean? If you want to, these are some additional things you could try:

• Optimize for speed.

Then please share your thoughts in a comment on the submission. Did this experiment make the code better? Worse? Did you learn anything from it?

## Source

JavaRanch Cattle Drive, exercise 6 http://www.javaranch.com/grains.jsp

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### grains-test.scm

``````;; Load SRFI-64 lightweight testing specification
(use-modules (srfi srfi-64))

;; Suppress log file output. To write logs, comment out the following line:
(module-define! (resolve-module '(srfi srfi-64)) 'test-log-to-file #f)

;; Require module
(use-modules (grains))

(test-begin "grains")

(test-eqv "square 1"
1
(square 1))

(test-eqv "square 2"
2
(square 2))

(test-eqv "square 3"
4
(square 3))

(test-eqv "square 4"
8
(square 4))

(test-eqv "square 16"
32768
(square 16))

(test-eqv "square 32"
2147483648
(square 32))

(test-eqv "square 64"
9223372036854775808
(square 64))

(test-eqv "total grains"
18446744073709551615
(total))

;; Tests go here

(test-end "grains")``````
``````(define-module (grains)
#:export (square total)

(define (square n)
(expt 2 (- n 1))
)

(define (total)
(- (expt 2 64) 1)
)``````