> wisp lives in the ST (optionally IO) monad. separate
> interpreters with completely segregated environments can be
> run concurrently. wisp has a few IO facilities, but they're
> completely sandboxed and can't accidentally affect the host
> program or environment.
This is wonderful. There's already an embedded R5RS Scheme for Haskell (http://hackage.haskell.org/package/husk-scheme) but it runs everything in the IO monad. That makes it fairly annoying for sandboxed embeddings.
Apart from its use of ST rather than IO, I'm curious how else Wisp compares to Husk. As far as I can tell, despite the name, Wisp appears to be a Lisp-1 (single namespace for functions and variables, no need to call "apply" or similar on variables referencing functions to call them).
It could be trivially implemented in Lua as a pre-processor. Lua has lambdas, higher level functions, lexical scope and tail call elimination.
The main problem is that it doesn't have a ternary operator, making conditional expression problematic to represent (you have to wrap an if statement in a lambda called on the fly).
For something more fully featured, see [0], it is written in MoonScript (which itself compiles to Lua), and the parser depends on LPeg, but writing a S-expression parser is rather easy.
Edit: There's also lcl [1], which is implemented in C. Written by lhf, one of the Lua authors. From the test files, it looks very basic.
(function()
if foo then return plus
else return minus
end
end)()(4, 6)
It is far too verbose to be used in manually crafted Lua, but acceptable if you treat it as a compiler target (with the caveat that the lambda creation will prevent LuaJIT from JITting that piece of code).
"A object-oriented, unicode-enabled lisp that compiles to and runs as fast as Lua. Equipped with macros and compile-time compiler manipulation. Comes with all built-in Lua functions."
ChibiScheme (https://code.google.com/p/chibi-scheme/) tries to be that. I've considered using it but have avoided it due to its relative newness and a few portability issues.
Unfortunately, Guile is both larger, and less portable than Lua. It's also licensed under the LGPL, which is harder (or impossible) to use in some environments than Lua's MIT-like license.
