Concerning erlang's bit syntax

[Magnus Thoang]

Hi,

I like erlang's bit syntax. It makes my life easier in almost all 
situations where I need to shuffle bytes around.

I was surprised, though, when the code I had ran in the erlang shell had 
to be rewritten for the compiler:

This matching works (R9C) in the shell but cannot be put in a module:

<<StrSize:32,Str:StrSize/binary,Rest/binary>> =
     <<0,0,0,6,$e,$r,$l,$a,$n,$g,1,2,3,4,5,6,7,8>>

When trying to compile the above expression, the compiler gives an error 
about StrSize being unbound (in the 'Str:StrSize/binary' expression).

The documentation is not clear about this case, but it mentions a 
somewhat similar function head as not being allowed.

It is just a minor annoyance, but is there a good reason for this?

-- 
Magnus Thoäng