[erlang-questions] Bit Syntax and compiler Erlang/OTP R21.1

Tue Aug 20 18:55:06 CEST 2019

On Tue, 20 Aug 2019 17:04:26 +0200
Valentin Micic <v@REDACTED> wrote:

> (tsdb_1_1@REDACTED)448> is_binary( <<0:1>> ).
> false

"is elephant?" is encoded in Erlang as: is_bitstring/1

75> is_bitstring(<<0:1>>).

> But, if you put two elephants next to each other, you get
> — a duck!
> is_binary( <<0:5, 0:3>> ). 
> true

Read "is_binary/1" as
"is_bitstring/1 and (bitlength_of(Elephants) mod 8 == 0)"


> Given all this, why would anyone find bitstrings useful?

That is why the default bitstring is a bytestring or
octetstring or binary:

98> is_binary(<<"blah">>) and is_binary(<<1, 2, 3>>).
is_binary(<<"blah">>) and is_binary(<<1, 2, 3>>).

As long as you do not tell the compiler to take bites of
memory that are no bytes, with that ":", the two of you seem
to agree there.

Might help when extracting flag bits? (or when talking to
some 9-bit byte PDP ... or was that 11? ... ;-) Anyway I
would rather deprecate and obsolete away dot notation for
record elements ...



Normality is merely a question of quantity,
not of quality.

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