Matching binary patterns with Erlang

29

Matching binary patterns with Erlang ☶ education erlang dev.to
authored by l1x 3 years ago | archive
Archive.org Archive.today Ghostarchive
| 10 comments

10

Using Erlang to parse NTP data

5

jmelesky 3 years ago | link

I have to say that I found erlang rather unwieldy as a language and environment, but I did love its binary pattern-matching. And I miss it whenever I’m parsing a binary file format.
1. 0
  l1x 3 years ago | link
  I agree. I am not sure why other languages do not implement this. I was trying to do the same with other languages and it is a hilariously complicated task. I mostly dislike two things about Erlang:
  
  OTP
  
  the lack of an easy way of creating a single binary from a project
  1. 5
    hauleth 3 years ago | link
    
    OTP
    
    Why? This is exactly what makes Erlang great.
    
    the lack of an easy way of creating a single binary from a project
    
    This is described into Erlang nature and one of the greatest features - hot upgrades.
    1. 1
      
      l1x 3 years ago | link
      
      Maybe it is just me. I need to spend more time on it. I never built anything that required OTP, and at the time I wanted to learn it I could not learn it fast enough.
      
      Hot upgrades sounds amazing in telco but in many industries, they want to have more control over what is running in production and have a solution to swap out the software using different methods.
      1. 2
        
        hauleth 3 years ago | link
        
        I never built anything that required OTP
        
        Supervisors are part of the OTP not “Erlang core”. gen_servers as well. So in Erlang virtually any application will use OTP.
3
hauleth 3 years ago | link
The greatest thing in pattern matching is that you can use previously matched numbers later, so if you have TLV encoded data then decoding it is a breeze, example:
```
decode(<<?int, Size:8, Num:Size/integer-unit:8>>) -> Num;
decode(<<?str, Size:8, Bin:Size/binary>>) -> Bin.
```
1. 2
  jimdigriz edited 3 years ago | link
  Depending on your requirements, you have to be careful with this as it is not efficient, so double check with:
  
  export ERL_COMPILER_OPTIONS=bin_opt_info
  
  As per http://erlang.org/doc/efficiency_guide/binaryhandling.html you should punt the X:Size into a binary match done in the function.
  
  For most though it won’t matter.
3

banjiewen 3 years ago | link

There are some fun caveats about performance with binary matching, too - this post is a decent overview of some of the gotchas.
1. 1
  
  l1x 3 years ago | link
  
  Thanks a lot! I am going to need this.
2

Hecate 3 years ago | link

I miss this syntax… I wish it was present i Haskell too!