[Haskell-cafe] Compiler's bane
andrewcoppin at btinternet.com
Wed Aug 27 15:59:28 EDT 2008
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!
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.
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
More information about the Haskell-Cafe