[Haskell-cafe] Compiler's bane
Neil Mitchell
ndmitchell at gmail.com
Wed Aug 27 16:08:51 EDT 2008
Hi
> I'm writing a simple interpretter for a small extended-lambda-calculus sort
> of language. And I'd just like to say... RECURSIVE LET-BINDS! GAAAAH!!! >_<
Agreed :-)
> To illustrate:
>
> let x = f x; y = 5 in x y
>
> A simple-minded interpretter might try to replace every occurrance of "x"
> with "f x". This yields
>
> let y = 5 in (f x) y
That's wrong, its a two step transformation. You just substitute all
occurances of x for f x:
let x = f (f x); y = 5 in (f x) y
For the case let x = 5 in x, you do the same thing:
let x = 5 in 5
Now as a second step you hoover up unused let bindings and disguard:
5
You seem to be combining the substitution and the removing of dead let
bindings, if you separate them you should have more luck.
Thanks
Neil
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