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-module(klsn_maybe). |
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-export([ |
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get_value/1 |
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, get_value/2 |
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, filtermap/2 |
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]). |
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%% A small helper module for working with the *Maybe* pattern |
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%% ({value, V} | none) that is defined in the klsn module itself. The functions |
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%% mirror common operations from the Haskell Maybe / Rust Option |
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%% family while keeping the interface idiomatic Erlang. |
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|
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-export_type([ |
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]). |
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%% @doc |
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%% Extract the wrapped value or raise badarg when *None* is supplied. |
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-spec get_value({value, Value}) -> Value. |
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get_value({value, Value}) -> |
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Value; |
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get_value(None) -> |
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erlang:error(badarg, [None]). |
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|
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%% @doc |
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%% Return the contained value when present, otherwise return *Default*. |
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-spec get_value |
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({value, Value}, Default::any()) -> Value; |
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(none, Default) -> Default. |
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get_value({value, Value}, _Default) -> |
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Value; |
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get_value(none, Default) -> |
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Default; |
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get_value(Arg1, Arg2) -> |
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erlang:error(badarg, [Arg1, Arg2]). |
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|
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|
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%% @doc |
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%% Combine filtering and mapping in one pass. When the callback returns |
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%% {value, V} the element is kept (and V becomes the new value); |
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%% returning none discards the element. |
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-spec filtermap(fun((any())->klsn:'maybe'(any())), list()) -> list(); |
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(fun((any(), any())->klsn:'maybe'(any())), map()) -> map(). |
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filtermap(Fun, List) when is_list(List) -> |
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lists:filtermap(fun(Val) -> |
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case Fun(Val) of |
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{value, Value} -> |
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{true, Value}; |
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none -> |
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false |
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end |
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end, List); |
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filtermap(Fun, Map) when is_map(Map) -> |
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maps:filtermap(fun(Key, Val) -> |
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case Fun(Key, Val) of |
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{value, Value} -> |
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{true, Value}; |
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none -> |
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false |
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end |
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end, Map). |