From 5a9cdd3cc89507d4d74f8bded56ce5e037b3b56e Mon Sep 17 00:00:00 2001
From: Trygve Laugstøl <trygvis@inamo.no>
Date: Fri, 23 Feb 2024 07:08:18 +0100
Subject: wip

---
 learn-you-some-erlang/hhfuns.erl | 111 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 learn-you-some-erlang/hhfuns.erl

(limited to 'learn-you-some-erlang/hhfuns.erl')

diff --git a/learn-you-some-erlang/hhfuns.erl b/learn-you-some-erlang/hhfuns.erl
new file mode 100644
index 0000000..ebe07a4
--- /dev/null
+++ b/learn-you-some-erlang/hhfuns.erl
@@ -0,0 +1,111 @@
+-module(hhfuns).
+-compile(export_all).
+
+one() -> 1.
+two() -> 2.
+
+add(X,Y) -> X() + Y().
+
+increment([]) -> [];
+increment([H|T]) -> [H+1|increment(T)].
+
+decrement([]) -> [];
+decrement([H|T]) -> [H-1|decrement(T)].
+
+
+map(_, []) -> [];
+map(F, [H|T]) -> [F(H)|map(F,T)].
+
+incr(X) -> X + 1.
+decr(X) -> X - 1.
+
+%% bases/1. Refered as the same function refactored in the book
+base1(A) ->
+    B = A + 1,
+    F = fun() -> A * B end,
+    F().
+
+%%% can't compile this one
+%% base(A) ->
+%%    B = A + 1,
+%%    F = fun() -> C = A * B end,
+%%    F(),
+%%    C.
+
+base2() ->
+    A = 1,
+    (fun() -> A = 2 end)().
+
+base3() ->
+    A = 1,
+    (fun(A) -> A = 2 end)(2).
+
+a() ->
+    Secret = "pony",
+    fun() -> Secret end.
+
+b(F) ->
+    "a/0's password is "++F().
+
+even(L) -> lists:reverse(even(L,[])).
+
+even([], Acc) -> Acc;
+even([H|T], Acc) when H rem 2 == 0 ->
+    even(T, [H|Acc]);
+even([_|T], Acc) ->
+    even(T, Acc).
+
+old_men(L) -> lists:reverse(old_men(L,[])).
+
+old_men([], Acc) -> Acc;
+old_men([Person = {male, Age}|People], Acc) when Age > 60 ->
+    old_men(People, [Person|Acc]);
+old_men([_|People], Acc) ->
+    old_men(People, Acc).
+
+filter(Pred, L) -> lists:reverse(filter(Pred, L,[])).
+
+filter(_, [], Acc) -> Acc;
+filter(Pred, [H|T], Acc) ->
+    case Pred(H) of
+        true  -> filter(Pred, T, [H|Acc]);
+        false -> filter(Pred, T, Acc)
+    end.
+
+%% find the maximum of a list
+max([H|T]) -> max2(T, H).
+
+max2([], Max) -> Max;
+max2([H|T], Max) when H > Max -> max2(T, H);
+max2([_|T], Max) -> max2(T, Max).
+
+%% find the minimum of a list
+min([H|T]) -> min2(T,H).
+
+min2([], Min) -> Min;
+min2([H|T], Min) when H < Min -> min2(T,H);
+min2([_|T], Min) -> min2(T, Min).
+
+%% sum of all the elements of a list
+sum(L) -> sum(L,0).
+
+sum([], Sum) -> Sum;
+sum([H|T], Sum) -> sum(T, H+Sum).
+
+fold(_, Start, []) -> Start;
+fold(F, Start, [H|T]) -> fold(F, F(H,Start), T).
+
+reverse(L) ->
+    fold(fun(X,Acc) -> [X|Acc] end, [], L).
+
+map2(F,L) ->
+    reverse(fold(fun(X,Acc) -> [F(X)|Acc] end, [], L)).
+
+filter2(Pred, L) ->
+    F = fun(X,Acc) ->
+            case Pred(X) of
+                true  -> [X|Acc];
+                false -> Acc
+            end
+        end,
+    reverse(fold(F, [], L)).
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