erlang - Understanding dialyzer result -

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i have following function:

-spec check_connection_header(list()) -> atom(). check_connection_header([{<<"connection">>, <<"close">>}|_]) ->     close;  check_connection_header([{<<"connection">>, <<"close">>}|_]) ->     close;  check_connection_header([{<<"connection">>, <<"close">>}|_]) ->     close;  check_connection_header([{<<"connection">>, <<"close">>}|_]) ->     close;  check_connection_header([_|rest]) ->     check_connection_header(rest);  check_connection_header([])->     keep_alive.

and when run dialyzer following output:

131: pattern [{<<67:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<99:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match type []  134: pattern [{<<67:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<67:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match type []  137: pattern [{<<99:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<99:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match type []  140: pattern [{<<99:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1,110:8/integer-unit:1,101:8/integer-unit:1,99:8/integer-unit:1,116:8/integer-unit:1,105:8/integer-unit:1,111:8/integer-unit:1,110:8/integer-unit:1>>, <<67:8/integer-unit:1,108:8/integer-unit:1,111:8/integer-unit:1,115:8/integer-unit:1,101:8/integer-unit:1>>} | _] can never match type []  143: pattern [_ | rest] can never match type []

i pretty new dialyzer , have trouble interpreting output of dialyzer. understand saying first 5 clauses of function can't match [], deliberate part since i'm matching empty list in sixth clause.

my erlang version erlang/otp 19.0 , dialyzer version v3.0.

a interesting discover dialyzer does'nt complain above code when run dialyzer v2.8 , erlang/otp 18 on machine.

things i've tried far:

  • i'm not experienced binaries in erlang initial thought had misunderstood binary pattern matching, seems not case. function passes test cases (calling function [] parameter no problem), , if replace binaries normal strings in function heads same complaints dialyzer.

  • rebuilt plt , cleaned project

thanks in advance

the reason dialyzer warnings function called [] due defect in code.

so conclude: dialyzer not wrong time either :)


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