[Haskell-cafe] Writing an interpreter for a language with mutability

Chris Wong lambda.fairy at gmail.com
Mon Dec 18 10:25:15 UTC 2017

Hi Jeremy,

I'm on my phone right now so I can't link, but try searching for "IORef"
and the "ST monad".


On Dec 18, 2017 10:06, "Jeremy Mikkola" <jeremy128 at gmail.com> wrote:

> I am quite certain I am not the first to try to do this, but my google-fu
> is failing me today.
> How does one go about interpreting a language with mutable objects in
> Haskell?
> The best approach I can think of is to represent the language's memory as
> a `Data.Map.Map RefID LanguageObject` where RefID is some type (probably
> Int) used as a reference. The LanguageObject structure might contain some
> values of type RefID to refer to other objects. Mutating an object involves
> simply replacing the value in the map at a given RefID.
> I don't like this approach for two reasons:
> 1. Map lookups aren't very efficient compared with actual references to
> the value.
> 2. I have to re-invent garbage collection, removing objects from the map
> when they no longer have incoming references. (Unlike simple interpreters
> for languages with immutable values, I can't rely on Haskell's garbage
> collector to do the work for me.)
> Is there a better approach?
> - Jeremy
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