On 03/25/2010 06:21 PM, Walter Bright wrote:
Ellery Newcomer wrote:
What do you think of Erlang's bit syntax if you've looked at it, or
could you if you haven't?
I know nothing about it.
I suppose you could think of it as sort of a regex-for-generic-data, but
you can use it as a pattern matcher or a data constructor.
The example Armstrong gives in Programming Erlang is
<<2#11111111111:11,B:2,C:2,_D:1,E:4,F:2,G:1,Bits:9>> = X
where X is assumedly a byte array or something.
the first 11 bits are asserted to be 1, and the remaining bits get
associated with the following variables.
Yeah, that example isn't much more impressive than bitfields.
You could do something like
<<N:32, Data:N/binary, _/binary>> = X
which would interpret the first four bytes as a length field, bind the
next N bytes to Data, and ignore the rest..
The general syntax for them should look something like
Bit: << >>
<< E >>
E: E , E1
E1
E1: Value
Value : Size
Value / TypeSpecList
Value : Size / TypeSpecList
//integral, fp, or binary (byte arrays, strings, etc) type
Value: Expression
// integral type
Size: Expression
TypeSpecList: TypeSpecList - TypeSpec
TypeSpec
TypeSpec: Endianness
Sign
Type
Unit
// default is big
Endianness: big
little
native
Sign: signed
unsigned
Type: integer
float
binary
//Size*Unit is the number of bits that get matched
// Unit defaults to 1 for Type = integer or float,
8 for Type = binary
Unit: IntegerLiteral
