[erlang-questions] Reia - Python/Ruby mix targeting Beam/HiPE

[Mikael Pettersson]

Bjorn Gustavsson writes:
 > "Gleb Peregud" <gleber.p@REDACTED> writes:
 > 
 > > According to http://wiki.reia-lang.org/wiki/Roadmap :
 > > The First Milestone: Compile to Erlang AST
 > > And I assume that Erlang AST does not permit mutable variables, hence
 > > it will probably not include mutable variables (unless hidden by Reia
 > > -> Erlang AST translator)
 > 
 > It should be trivial to implement mutable variables, simply by inventing
 > a new, unused variable name each time a mutable variable is assigned.
 > (Further references to the mutable variable should be changed to refer
 > to the new name, of course.)

Define "mutable variable". I know of (at least) two different kinds:

1. Each variable binding starts a new scope, nested within but
   otherwise independent of the previous/surrounding scope.
   This is what SML's LET and Scheme's LET* implement.
   It's still purely functional and can be implemented via
   a simple renaming operation (alpha conversion).

2. A variable is bound to an updateable memory cell, and assignment
   updates that cell, like in C/Pascal/etc. If these cells can escape
   (e.g. via closures), then simple renaming doesn't suffice, and
   you're really forced to have a mutable store. Stores can be
   emulated in the Erlang VM, but it won't be cheap.