[erlang-questions] Reassigning variables

Gaspar Chilingarov <>
Wed Mar 18 13:38:19 CET 2009

I'm totally agree with you, Richard!

Even in complex project I had practically no need of reassignment.

1. There is a nested calls which is possible to format nicely
         f3( Args )

2. If you need complex and very flexible solution - implement simple
stack machine - you pass to the interpreter 2 lists - list of functions
to be called, the initial stack (well, I've beed passing there also
application/process global state variable)

As a single processing function result you get:
{continue, NewStack, NewState} - continue applying next command in a
command list
{error, ErrorMsg, NewState} - stop processing and throw a message (we
got an error)
{ok, Result, NewState} - stop processing and return some value to
calling function.

It's rather easy to write/debug such kind of interpreter and then
describe ALL necessary logic in that interpreter.

(We had an interpreter for web-based application - form
generation/validation/submit processing and etc).
We also described all the periodic tasks occurring in the system as a
such command list (btw closures+mnesia rule in term of keeping
application state intact for further processing).

Well :) It took 2 software revisions to get there :) Using
positional/named registers was too hard and messing all the things up.

Tip: for easier processing attach to variables in stack their type -
which will make finding errors in your processing chains easier.

Gaspar Chilingarov

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