-
Notifications
You must be signed in to change notification settings - Fork 5
/
chp4.erl
57 lines (46 loc) · 1.59 KB
/
chp4.erl
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
-module(chp4).
-export([append/2, take/2, drop/2, reverse/1, sort/1, force/1]).
-compile(export_all).
%% append two streams together
append([], []) -> [];
append([], [H|T]) -> [ H | fun() -> append([], T) end ];
append([X | S], T) -> [ X | fun() -> append(S, T) end ].
%% take the first N elements from a stream
take(0, _L) -> [];
take(_N, []) -> [];
take(N, [H|T]) ->
[H | fun() -> take(N-1, T) end].
%% drop the first N elements from a stream
%drop(0, L) -> L;
%drop(_N, []) -> [];
%drop(N, [_H|T]) ->
% [T | fun() -> drop(N-1, T) end].
%% the monolithic example from pg 35
%% suspend the drop call, but perform it at once when forced
drop(N, L) ->
Dprime = fun(0, Lprime, _F) -> Lprime;
(_N, [], _F) -> [];
(Nprime, [_H|T], F) -> F(Nprime-1, T, F) end,
fun() -> Dprime(N, L, Dprime) end.
%% monolithic version of reverse
reverse(L) ->
Rprime = fun([], Rev, _F) -> Rev;
([H|T], Rev, F) -> F(T, [H | Rev], F) end,
fun() -> Rprime(L, [], Rprime) end.
%% Exercise 4.2 - Insertion sort on streams.
sort([]) -> [];
sort(L) ->
io:format("Cur L: ~p~n", [L]),
Min = lists:min(L),
[ Min | fun() -> sort(remove_val(Min, L)) end ].
remove_val(X, L) ->
remove_val(X, L, []).
remove_val(_X, [], L) -> lists:reverse(L);
remove_val(X, [X|T], L) -> lists:reverse(L, T); % reverse L and append T
remove_val(X, [H|T], L) -> remove_val(X, T, [H|L]).
%% force evaluation of the next unit of the stream
force([]) -> [];
force(Fun) when is_function(Fun) -> Fun();
force([_X, Fun | []]) when is_function(Fun) -> Fun();
force([_X|T]) ->
force(T).