first commit

.gitignore

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+*.beam
+.*

chapter_1/boolean.erl

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+-module(boolean).
+-export([b_not/1, b_and/2, b_or/2]).%, b_nand/2]).
+
+b_not(true) -> false;
+b_not(false) -> true.
+
+b_and(true, true) -> true;
+b_and(_, _) -> false.
+
+b_or(true, _) -> true;
+b_or(_, true) -> true;
+b_or(_, _) -> false.

chapter_1/demo.erl

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+-module(demo).
+-export([double/1, area/1]).
+
+double(Value) -> times(Value, 2).
+times(X, Y) -> X * Y.
+
+area(sharp) -> {sharp, 1};
+area(Other) -> {sharp, Other}.

chapter_2/db.erl

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+-module(db).
+-export([new/0, destroy/1, write/3, delete/2, read/2, match/2]).
+
+new() -> [].
+destroy(_Db) -> successful.
+
+write(Key, Val, Db) -> [{Key, Val} | Db].
+
+delete(_Key, []) -> [];
+delete(Key, [{HK, _}|T]) when Key == HK -> delete(Key, T);
+delete(Key, [H|T]) -> [H|delete(Key, T)].
+
+read(_Key, []) -> {error, instance};
+read(Key, [{H_Key, Val}|_T]) when Key == H_Key -> {ok, Val};
+read(Key, [_H|T]) -> read(Key, T).
+
+match(_Val, []) -> [];
+match(Val, [{H_Key, H_Val} | T]) when H_Val == Val -> [H_Key | match(Val, T)];
+match(Val, [_H|T]) -> match(Val, T).

chapter_2/every.erl

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+-module(every).
+-export([add_one/1, avg/1, even/1, member/2, sum_acc/2, bump/2]).
+
+add_one([]) -> [];
+add_one([H|T]) -> [H + 1 | add_one(T)].
+
+%bump([], List) -> reverse(List);
+bump([H|T], List) -> bump(T, [H+1|List]).
+
+avg(List) -> sum(List) / len(List).
+
+sum([])    -> 0;
+sum([H|T]) -> H + sum(T).
+
+len([])    -> 0;
+len([_|T]) -> 1 + len(T).
+
+even([]) -> [];
+even([Head | Tail]) when Head rem 2 == 0 -> [Head | even(Tail)];
+even([_ | Tail]) -> even(Tail).
+
+member(_, []) -> false;
+member(Item, [H|_]) when Item == H -> true;
+member(Item, [_|T]) -> member(Item, T).
+
+sum_acc([], Sum) -> Sum;
+sum_acc([H|T], Sum) -> sum_acc(T, Sum + H).

chapter_2/example.erl

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+-module(example).
+-export([even/1, number/1]).
+
+even(Int) when Int rem 2 == 0 -> true;
+even(Int) when Int rem 2 == 1 -> false.
+
+number(Num) when is_integer(Num) -> interger;
+number(Num) when is_float(Num) -> float;
+number(_Other) -> false.
+

chapter_2/exec.erl

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+-module(exec).
+-export([sum/1, sum/2, create/1]).
+
+% 练习3-1 表达式求值
+sum(1) -> 1;
+sum(I) when I > 0 -> I + sum(I - 1);
+sum(_) -> {error, "less one"}.
+
+sum(N, M) when N > M -> exit("N > M");
+sum(N, N)            -> N;
+sum(N, M) -> N + sum(N + 1, M).
+
+create(0) -> [];
+create(C) when C > 0 -> [C | create(C - 1)].

chapter_2/list.erl

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+-module(list).
+-compile(export_all).
+
+filter([], _N) -> [];
+filter([H|T], N) when H =< N -> [H | filter(T, N)];
+filter([_H|T], N) -> filter(T, N).
+
+reverse(List) -> reverse(List, []).
+
+% Good Job 要多使用尾递归
+reverse([], R) -> R;
+reverse([H|T], R) -> reverse(T, [H|R]).
+
+concatenate([], R) -> reverse(R);
+concatenate([[]|Ty], R) -> concatenate(Ty, R);
+concatenate([[H|Tx]|Ty], R) -> concatenate([Tx|Ty], [H|R]).
+