Meta.parse supports interpolation?

New to Julia
1

It is confusing for me when I use Meta.parse() function as:

Julia> x = 2
Julia> Meta.parse(":(:(v = $x))")
:($(Expr(:quote,:($(Expr(quote,:(v = 2)))))))

In general, an interpolation with single $ in :(:($x)) should not interpolate the value of x (which is 2 in the above example).
Since the manual doesn’t mention the case, is this rule special to Meta.parse() function?

2

It’s just doing string interpolation before Meta.parse is called at all, and doesn’t care what the string contains:

julia> x = 2;

julia> ":(:( :) v = $x )])" # nonsense
":(:( :) v = 2 )])"

julia> Meta.parse(ans)
ERROR: Base.Meta.ParseError("missing comma or ) in argument list")
3 Likes
3

Oh, you are right, I have totally forgotten the string interpolation!

4

By the way, is there any method to use Meta.parse to parse such form as:

":(:(v = $x))"

to see how Julia transform into internal AST form?

5

The issue is on string, so you just need to produce the correct string. You can escape $ with \$.

1 Like
6

You might also be interested in the Meta.@dump macro, which prints the AST you give it, so you could do e.g. Meta.@dump :(v = $x) to inspect the AST. If you want to know how these are actually generated internally, I’m afraid, you will have to learn Lisp.

1 Like