Colin Caine (Feb 27 2021 at 19:40): Colin Caine (Feb 27 2021 at 19:40):I'd like to be able to have an environment where only symbols I specify are defined.
This is for an educational purpose where I want to define
E.g. an environment with only a nand(a, b) function and then the user is expected to define a bunch of combinatorial logic from that.
Mason Protter (Feb 27 2021 at 19:44):Have you looked into baremodule?
Colin Caine (Feb 27 2021 at 19:44):Yeah, but it still imports too much.
Mason Protter (Feb 27 2021 at 19:45):How is the user meant to interact with Julia?
Mason Protter (Feb 27 2021 at 19:45):It sounds like maybe you just should make a little DSL
Colin Caine (Feb 27 2021 at 19:47):The idea was to just get Julia semantics but with a clean slate that doesn't contain any of Core or Base.
Behind the scenes, they're still there, but the user can only interact with the names I give them or that they define themselves.
Colin Caine (Feb 27 2021 at 19:48):Maybe I can just build some machinery that tracks what symbols are in use and an eval that errors if you use any "undefined" symbol.
Mason Protter (Feb 27 2021 at 19:48):Again, how is the user meant to interact? repl? Some input box on a website?
Mason Protter (Feb 27 2021 at 19:48):Colin Caine said:
Maybe I can just build some machinery that tracks what symbols are in use and an eval that errors if you use any "undefined" symbol.
yeah, that's what I meant by a "little dsl"
Colin Caine (Feb 27 2021 at 19:50):As for input, files and a REPL.
Mason Protter (Feb 27 2021 at 20:00):What names are in a baremodule that you don't want? I think you might be able to get away with just using a baremodule and then having a blacklist for the remaining names, e.g. Core and eval
Colin Caine (Feb 27 2021 at 20:23):I think I'd just want to expose nand(a, b), true and false. And all of the string and number literals would be absent.
Small languages are used a lot in some programming courses (e.g. Beginner's Student Language defined in racket), though I'm not sure one as basic as I'm suggesting would actually be helpful :)
Colin Caine (Feb 27 2021 at 20:25):Anyway, this doesn't seem super hard, maybe I'll just build something and see if it's easy and useful.
Mason Protter (Feb 27 2021 at 20:44):Okay, here's a demo with ReplMaker.jl that I think works:
using ReplMaker, MLStyle
baremodule Sandbox end
@eval Sandbox nand(x, y) = $(!)($(&)(x, y))
function sandbox_parser(s::String)
ex = Meta.parse(s)
filterer(ex) = @match ex begin
:Core => println("that's not allowed")
:eval => println("that's not allowed")
x::Bool => x
::Number => println("that's not allowed")
::String => println("that's not allowed")
::AbstractArray => println("that's not allowed")
x::Expr => Expr(x.head, filterer.(x.args)...)
x => x
end
:(@eval Sandbox $(filterer(ex)))
end
function valid_julia(s)
input = String(take!(copy(ReplMaker.LineEdit.buffer(s))))
ex = Meta.parse(input)
if ex isa Expr && ex.head == :incomplete
false
else
true
end
end
sandbox_mode = initrepl(sandbox_parser;
prompt_text="Sandbox> ",
prompt_color = :yellow,
startup_text = false,
mode_name = :sandbox,
valid_input_checker = valid_julia)
enter_mode!(sandbox_mode)
if you run that, you'll find yourself in the sandbox> prompt and then you can run various stuff:
Sandbox> t = true; f = false;
Sandbox> nand(t,t)
false
Sandbox> nand(f,f)
true
Sandbox> not(x) = nand(x, true)
not (generic function with 1 method)
Sandbox> and(x, y) = not(nand(x, y))
and (generic function with 1 method)
Sandbox> and(t, t)
true
Sandbox> 1
that's not allowed
That's very neat. I was thinking I would have to do some name mangling as well as pattern matching
Mason Protter (Feb 27 2021 at 20:53):One potential issue is that they can always just hit the backspace button to exit the prompt and then do whatever they want
Mason Protter (Feb 27 2021 at 20:54):but I think you could delve into sandbox_mode.keymap_dict and potentially remove that ability? I'm not sure.
Mason Protter (Feb 27 2021 at 20:55):Maybe safer would be to just make your own barebones repl that they can't escape from?
Mason Protter (Feb 27 2021 at 20:56):https://github.com/hanslub42/rlwrap will make it somewhat easy to make your own repl that supports things like history and such
Colin Caine (Feb 27 2021 at 20:58):Yeah, there's a few other things, like you can still import whatever modules you like, and there's some more tricky security things if I wanted to make a more secure sandbox.
But this is a very nice start, thank you :)
Mason Protter (Feb 27 2021 at 20:59):Mhm. You'd want to blacklist using and import for sure.
Mason Protter (Feb 27 2021 at 21:00):I wonder if there's a way to remove all the names from Core, but still allow them to be defined, just not used.
Mason Protter (Feb 27 2021 at 21:12):I opened a discourse thread asking if anyone knows a way. https://discourse.julialang.org/t/even-more-bare-baremodule/56156
Mason Protter (Feb 27 2021 at 21:13):An alternative to a real module would be to repurpose some of the code from StaticModules.jl to make your own custom 'module' that does exactly what you want
Takafumi Arakaki (tkf) (Feb 27 2021 at 22:16):I guess you'd also need to exclude Main, as otherwise, I can call, e.g., Main.Base.eval.
Takafumi Arakaki (tkf) (Feb 27 2021 at 22:16):As a related note, I'm somewhat surprised that names(Sandbox; all = true, imported = true) does not output anything.
Takafumi Arakaki (tkf) (Feb 27 2021 at 22:21):Oh, it also looks like you can ccall inside a baremodule (since it's a syntax).
Colin Caine (Feb 27 2021 at 22:22):names(Sandbox) does give output for me on Julia 1.5
Takafumi Arakaki (tkf) (Feb 27 2021 at 22:25):Ah, I wasn't accurate. I meant to say an array with more than one element; e.g., I was hoping to see Array etc.
Colin Caine (Feb 27 2021 at 22:26):At least a couple of months ago there were some quite big differences between the output of Meta.parse on 1.5 and 1.6 (with 1.6 giving lowered IR for some things). I wonder if that was ever cleared up.
Colin Caine (Feb 27 2021 at 22:26):@Takafumi Arakaki (tkf) ah, gotcha.
Colin Caine (Feb 27 2021 at 23:05):Expanded on @Mason Protter's example :)
using ReplMaker, MLStyle
baremodule Sandbox end
@eval Sandbox nand(x, y) = $(!)($(&)(x, y))
function eval_in_sandbox(ex)
forbidden_names = setdiff(names(Core; all=true, imported=true), names(Sandbox; all=true, imported=true))
filterer(ex) = @match ex begin
x::Bool => x
x::LineNumberNode => x
# Ban everything.
# Copy anything you want to allow to above this point.
# it's a bit complicated to work out when a symbol is being used as a
# reference and what scope it is in. I think the JuliaVariables people
# have maybe done something with that?
s::Symbol => s in forbidden_names ? throw("Sorry! You can't use that name in the sandbox") : s
# Not allowed to import stuff
Expr(:using, _...) ||
Expr(:import, _...) => error("Imports are not permitted in the sandbox")
# Julia literals, these are mostly or entirely harmless (I think)
# but you might want to omit them or rewrite them to something else or whatever.
::Bool ||
::Number ||
::String ||
Expr(:string, _...) || # string interpolation
::QuoteNode ||
Expr(:quote, _...) ||
Expr(:ref, _...) || # a[i], but also Int[]
Expr(:typed_vcat, _...) ||
Expr(:typed_hcat, _...) ||
Expr(:vect, _...) ||
Expr(:vcat, _...) ||
Expr(:hcat, _...) ||
Expr(:tuple, _...) || # also covers named tuples
Expr(:comprehension, _...) ||
Expr(:typed_comprehension, _...) ||
Expr(:generator, _...) => error("This literal is not permitted in the sandbox")
# TODO
# ccall (!!)
# Recurse
# Expr(head, args...) => Expr(head, filterer.(x.args)...)
x::Expr => Expr(x.head, filterer.(x.args)...)
# Fallback for other things
x => error("Unknown thing: $x")
end
:(@eval Sandbox $(filterer(ex)))
end
function sandbox_parser(s::String)
ex = Meta.parse(s)
eval_in_sandbox(ex)
end
function valid_julia(s)
input = String(take!(copy(ReplMaker.LineEdit.buffer(s))))
ex = Meta.parse(input)
!(ex isa Expr && ex.head == :incomplete)
end
sandbox_mode = initrepl(sandbox_parser;
prompt_text="Sandbox> ",
prompt_color = :yellow,
startup_text = false,
mode_name = :sandbox,
valid_input_checker = valid_julia)
enter_mode!(sandbox_mode)
I guess what I should actually do is just transparently rewrite symbols that match anything in Core. That would be quite simple.
Colin Caine (Feb 28 2021 at 00:44):For posterity: I posted a better version on discourse.
Colin Caine (Feb 28 2021 at 17:49):I made a little package for fun https://github.com/cmcaine/Sandboxes.jl
Last updated: Oct 02 2023 at 04:34 UTC