In order to run, log in to csci4409, create a directory with your
name, copy the file below with the name pm.erl. In that
directory type erl to start the Erlang shell, then
type c(pm). (don't
forget the period at the end). To call the functions, use the prefix
pm: pm:filter. I recommend opening two windows: one to
edit the file, one to run the shell. Use Ctrl-C to stop anything
problematic. Use Ctrl-C followed by q, or Ctrl-G, return, q, to quit.
-module(pm). % pattern-matching module
% export functions, specify number of arguments:
-export([sum/1,count/2,filter/2,filterLarge/2,equalsTwo/1,
equalsTwoGuard/1).
-import(lists, [append/2]).
%%%%% Simple examples
equalsTwo(2) -> true;
equalsTwo(_) -> false.
%%%% This function works only on numbers
equalsTwoGuard(2) -> true;
equalsTwoGuard(X) when is_number(X) -> false.
%%%%% List functions using pattern-matching
sum([H|T]) -> H + sum(T);
sum([]) -> 0.
count([H|T],H) -> 1 + count(T,H);
count([_|T],H) -> count(T,H);
count([],_) -> 0.
filter([E|T],E) -> filter(T,E);
filter([H|T],E) -> [H|filter(T,E)];
filter([],_) -> [].
%%%%% write a function replace that takes a list and
%%%%% two numbers and replaces all occurrences of
%%%%% the first numbers in the list by the second one
%%%%% using guards
filterLarge([H|T],E) when H > E -> filterLarge(T,E);
filterLarge([H|T],E) -> [H|filterLarge(T,E)];
filterLarge([],_) -> [].
%%%%% Write a function that counts even numbers in a list
%%%%% Use rem for remainder and == for comparison
%%%%% Write a function isSorted that takes a list of
%%%%% numbers and returns true if it is sorted in non-decreasing
%%%%% order, false otherwise
%%%%% Write a function to reverse a list. Do not use
%%%%% the predefined reverese, although you may use a predefined
%%%%% append (imported)