You can get rid of all recursive bindings by transforming them into a
use of a fixpoint combinator.
And then you can use a non-recursive definition of the fixpoint
combinator, and never worry about recursive bindings again.
-- Lennart
On Wed, Aug 27, 2008 at 8:59 PM, Andrew Coppin
Hi guys.
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!!! >_<
No other part of the program has consumed nearly as much brain power as me trying to figure out when it is and isn't safe to replace a variable with its RHS.
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
...and x is now a free variable. OOPS!
Trying to tease out exactly under which conditions you can and cannot perform the substitution is utterly maddening. Since this is a Haskell mailing list and as such it is populated by vast numbers of people with PhDs and so forth... does anybody happen to know the *correct* solution to this conundrum? Before I become clinically insane...? o_O
By the way... To all those people who work on projects like GHC and so on, who have to get this stuff right "for real": you have my infinite respect!
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