Functional Erlang Assignment 1

assignment1.erl

-module(assignment1).
-include_lib("eunit/include/eunit.hrl").
-export([hypotenuse/2, area/1, perimeter/1, enclose/1, bits/1, bits_tail/1]).

% You can run test with:
% c(assignment1).
% assignment1:test().

% Available shapes:
% {circle, {X,Y}, R}
% {rectangle, {X,Y}, H, W}
% {triangle, {X1,Y1}, {X2,Y2}, {X3,Y3}}

% Define a function perimeter/1 which takes a shape 
%   and returns the perimeter of the shape.
% Choose a suitable representation of triangles, 
%   and augment area/1 and perimeter/1 to handle this case too.
% Define a function enclose/1 that takes a shape 
%   and returns the smallest enclosing rectangle of the shape.

% Find line length by two coords
hypotenuse({X1,Y1}, {X2,Y2}) ->
    math:sqrt((X2-X1)*(X2-X1) + (Y2-Y1)*(Y2-Y1)).

% Assignment

% Area of a shape
area({circle, {_X,_Y}, R}) ->
    math:pi() * R*R;

area({rectangle, {_X,_Y}, H, W}) ->
    H * W;

area({triangle, {X1,Y1}, {X2,Y2}, {X3,Y3}}) ->
    % 2D vector cross-product, is area of parallelogram
    abs(((X2-X1)*(Y3-Y1) - (X3-X1)*(Y2-Y1)) / 2).

% Perimeter of a shape
perimeter({circle, {_X,_Y}, R}) ->
    2*math:pi()*R;

perimeter({rectangle, {_X,_Y}, H, W}) ->
    2*H + 2*W;

perimeter({triangle, {X1,Y1}, {X2,Y2}, {X3,Y3}}) ->
    hypotenuse({X1,Y1}, {X2,Y2}) +
    hypotenuse({X1,Y1}, {X3,Y3}) +
    hypotenuse({X2,Y2}, {X3,Y3}).

% Enclose rectangle of a shape
enclose({circle, {X,Y}, R}) ->
    {rectangle, {X-R, Y-R}, 2*R, 2*R};

enclose({rectangle, {X,Y}, H, W}) ->
    {rectangle, {X,Y}, H, W};

enclose({triangle, {X1,Y1}, {X2,Y2}, {X3,Y3}}) ->
    X_MIN=lists:min([X1, X2, X3]),
    X_MAX=lists:max([X1, X2, X3]),
    Y_MIN=lists:min([Y1, Y2, Y3]),
    Y_MAX=lists:max([Y1, Y2, Y3]),

    % Find dimensions of enclosing rectangle and put in a left bottom coord of the triangle
    {rectangle, {X_MIN,Y_MIN}, Y_MAX-Y_MIN, X_MAX-X_MIN}.

% Find sum of bits, direct recursive
bits(0) -> 0;
bits(X) -> (X band 1) + bits(X bsr 1).

% Find sum of bits, tail recursive

bits_tail(X) -> bits_tail(X, 0).

bits_tail(0, ACC) -> ACC;
bits_tail(X, ACC) -> bits_tail(X bsr 1, ACC + (X band 1)).

% All tests
hypotenuse_test() -> ?assert(hypotenuse({4,1},{1,5}) == 5).

area_test() -> [
    ?assert(area({circle, {0,0}, 1}) == math:pi()),
    ?assert(area({rectangle, {0,0}, 2, 3}) == 6),
    ?assert(area({triangle, {1,5}, {4,5}, {4,1}}) == 6)
].

perimeter_test() -> [
    ?assert(perimeter({circle, {0,0}, 1}) == 2 * math:pi()),
    ?assert(perimeter({rectangle, {0,0}, 2, 3}) == 10),
    ?assert(perimeter({triangle, {1,5}, {4,5}, {4,1}}) == 12)
].

enclose_test() -> [
    ?assert(enclose({circle, {1,1}, 1}) == {rectangle, {0,0}, 2, 2}),
    ?assert(enclose({rectangle, {0,0}, 2, 3}) == {rectangle, {0,0}, 2, 3}),
    ?assert(enclose({triangle, {1,5}, {4,5}, {4,1}}) == {rectangle, {1,1}, 4, 3})
].

bits_test() -> [
    ?assert(bits(7) == 3),
    ?assert(bits(8) == 1)
].

bits_tail_test() -> [
    ?assert(bits_tail(7) == 3),
    ?assert(bits_tail(8) == 1)
].