Way to get string representation of an Expression?

General Usage
1

Let’s say you have a deeply nested Expr node.

How do you turn that into a string that could (manually) be copied and pasted into the REPL?

edit: related github issue#25121

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2

string?

3

The output from string() sometimes looks like:

$(Expr(:stagedfunction, :(dcontract(S1::FourthOrderTensor{dim}, S2::FourthOrderTensor{dim}) where dim), quote  # none, line 3:
    TensorType = getreturntype(dcontract, get_base(S1), get_base(S2)) # none, line 4:
    ...
    exps = Expr(:tuple) # none, line 7:
    for l = 1:dim, k = 1:dim, j = 1:dim, i = 1:dim # none, line 8:
        ex1 = (Expr[(Core._expr)(:ref, $(Expr(:copyast, :($(QuoteNode(:(get_data(S1))))))), idxS1(i, j, m, n)) for m = 1:dim, n = 1:dim])[:] # none, line 9:
        ex2 = (Expr[(Core._expr)(:ref, $(Expr(:copyast, :($(QuoteNode(:(get_data(S2))))))), idxS2(m, n, k, l)) for m = 1:dim, n = 1:dim])[:] # none, line 10:
        push!(exps.args, reducer(ex1, ex2, true))
    end # none, line 12:
    expr = remove_duplicates(TensorType, exps) # none, line 13:
    (Core._expr)(:block, $(Expr(:copyast, :($(QuoteNode(:( # none, line 14:)))))), Expr(:meta, :inline), $(Expr(:copyast, :($(QuoteNode(:( # none, line 15:)))))), (Core._expr)(:macrocall, Symbol("@inbounds"), (Core._expr)(:return, (Core._expr)(:call, TensorType, expr))))
end))

Isn’t there enough information there to make a string without just being an Expr with quotes around it?

// edit: a simpler example would be:

julia> parse("import Woof; import Bowow")

:($(Expr(:toplevel, :(import Woof), :(import Bowow))))

similar posts:

4

I guess the real questions now are:

// just wanted to do the research before I try to code something up

5

If you just want to paste it into the repl and you have the expression available you can do that without turning it into a string first - just use eval.

Other than that, string is probably what you’re looking for. Sometimes the result looks a bit arcane, but you should be able to eval it. For example,

julia> eval(:($(Expr(:toplevel, :(import Woof), :(import Bowow)))))
ERROR: ArgumentError: Module Woof not found in current path.
Run `Pkg.add("Woof")` to install the Woof package.
Stacktrace:
 ...

If you wanted to do source to source translation, I believe CSTParser is currently the most capable package, but that’s probably not what you’re looking for.

6

That is what I’m after. I was just wondering if anyone has made some headway on it.

see: Difference b/w include("foo.jl") and eval(parse(readstring(open( "foo.jl" ))))

7

As I found somewhere on them internets, you can use Base.show_unquoted to convert any Expr to a string of valid Julia code:

julia> Base.show_unquoted(stdout, :(import Woof; import Bowow))
begin
    import Woof
    #= REPL[5]:1 =#
    import Bowow
end

To convert to a string, use IOBuffer, or write to a file:

julia> buf = IOBuffer();

julia> Base.show_unquoted(buf, :(import Woof; import Bowow))

julia> String(take!(buf))
"begin\n    import Woof\n    #= REPL[11]:1 =#\n    import Bowow\nend"
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