92 lines
2.5 KiB
Erlang
92 lines
2.5 KiB
Erlang
% @doc called ltr to disambiguate from "char"
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%
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% In "A + B + AB", this is one of the individual letters.
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%
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% a letter is a binary. atom is more natural representation but this is http,
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% can't be spamming the atoms table.
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%
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% mathematically, this is a variable like "a", "b", "c", etc
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-module(wfc_ltr).
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-export_type([
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ltr/0
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]).
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-export([
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validate/1,
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from_binary/1, to_binary/1
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]).
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% @doc
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% a character is binary data that would be a valid atom
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%
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% [a-z][A-Za-z0-9_]+
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%
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% - leads with lowercase letter
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% - underscores ok
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% - numbers ok
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% - no non-ascii chars
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-opaque ltr() :: {c, binary()}.
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%%-----------------------
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%% constructors/destructors
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%%-----------------------
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-spec validate(Ltr) -> Result
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when Ltr :: ltr(),
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Result :: ok
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| {error, Reason :: string()}.
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% @doc validate if a candidate ltr is well-formed and the inner binary is
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% legal
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validate({c, Binary}) ->
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case from_binary(Binary) of
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{ok, {c, X}} when X =:= Binary ->
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ok;
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Error ->
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Error
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end;
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validate(Term) ->
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Error = wfc_utils:emsg("wfc_ltr:validate failed; malformed ltr: ~p", [Term]),
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{error, Error}.
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-spec from_binary(Binary) -> Result
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when Binary :: binary(),
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Result :: {ok, ltr()}
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| {error, Reason :: string()}.
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% @doc
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% make sure the binary is a legal ltr and wrap it in a {c, Binary} tuple
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% @end
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%% initial char must be [a-z]
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from_binary(<<L:8, Rest/binary>>) when $a =< L, L =< $z ->
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new2(<<L>>, Rest);
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from_binary(Char = <<L:8, _/binary>>) ->
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{error, wfc_utils:emsg("wfc_ltr:from_binary(~p): illegal lead character: ~p", [Char, L])};
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from_binary(Char) ->
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wfc_utils:err("wfc_ltr:from_binary(~p): malformed argument", [Char]).
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%% rest must be [A-Za-z0-9_]
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new2(Acc, <<L:8, Rest/binary>>) when ($A =< L andalso L =< $Z)
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orelse ($a =< L andalso L =< $z)
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orelse ($0 =< L andalso L =< $9)
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orelse (L =:= $_) ->
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new2(<<Acc/binary, L>>, Rest);
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new2(Acc, <<>>) ->
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{ok, {c, Acc}};
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new2(Acc, Rest = <<BadChar:8, _/binary>>) ->
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WholeChar = <<Acc/binary, Rest/binary>>,
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Error = wfc_utils:emsg("wfc_ltr:new2(~p, ~p): illegal character in ltr: ~p; WholeChar: ~p", [Acc, Rest, BadChar, WholeChar]),
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{error, Error}.
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-spec to_binary(ltr()) -> Result
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when Result :: {ok, binary()}
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| {error, string()}.
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to_binary({c, X}) -> {ok, X};
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to_binary(Bad) -> {error, wfc_utils:str("wfc_ltr:to_binary: bad letter: ~tp", [Bad])}.
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