AST example in julia

New to Julia
1

Hi,

I was trying to generate the AST for the following code snippet:

function alma(c)
    f(x,y) = 3x + 4y
    A = Int8[1, 2, 3] * c
    B = [4.0, 5.0, 6.0] .+ c
    return f(A,B)/c
end

str = open(f->read(f, String), "expr.jl")
ex = Meta.parse(str)
dump(ex)

I got the following:

Expr
  head: Symbol function
  args: Array{Any}((2,))
    1: Expr
      head: Symbol call
      args: Array{Any}((2,))
        1: Symbol alma
        2: Symbol c
    2: Expr
      head: Symbol block
      args: Array{Any}((8,))
        1: LineNumberNode
          line: Int64 2
          file: Symbol none
        2: Expr
          head: Symbol =
          args: Array{Any}((2,))
            1: Expr
              head: Symbol call
              args: Array{Any}((3,))
                1: Symbol f
                2: Symbol x
                3: Symbol y
            2: Expr
              head: Symbol block
              args: Array{Any}((2,))
                1: LineNumberNode
                2: Expr
        3: LineNumberNode
          line: Int64 3
          file: Symbol none
        4: Expr
          head: Symbol =
          args: Array{Any}((2,))
            1: Symbol A
            2: Expr
              head: Symbol call
              args: Array{Any}((3,))
                1: Symbol *
                2: Expr
                3: Symbol c
        5: LineNumberNode
          line: Int64 4
          file: Symbol none
        6: Expr
          head: Symbol =
          args: Array{Any}((2,))
            1: Symbol B
            2: Expr
              head: Symbol call
              args: Array{Any}((3,))
                1: Symbol .+
                2: Expr
                3: Symbol c
        7: LineNumberNode
          line: Int64 5
          file: Symbol none
        8: Expr
          head: Symbol return
          args: Array{Any}((1,))
            1: Expr
              head: Symbol call
              args: Array{Any}((3,))
                1: Symbol /
                2: Expr
                3: Symbol c

The return expression is wrong. Is this a bug or it should put this out?

Regards,
RUn

2

Please, read dump documentation that says:

dump(x; maxdepth=8)

Show every part of the representation of a value. The depth of the output is
truncated at maxdepth.

You are seeing empty Exprs because dump has truncated the output.

2 Likes
3

You can obtain the AST in an easy way by constructing a quoted expression

julia> ex = quote
           function alma(c)
               f(x,y) = 3x + 4y
               A = Int8[1, 2, 3] * c
               B = [4.0, 5.0, 6.0] .+ c
               return f(A,B)/c
           end
       end
quote
    #= REPL[6]:2 =#
    function alma(c)
        #= REPL[6]:2 =#
        #= REPL[6]:3 =#
        f(x, y) = begin
                #= REPL[6]:3 =#
                3x + 4y
            end
        #= REPL[6]:4 =#
        A = Int8[1, 2, 3] * c
        #= REPL[6]:5 =#
        B = [4.0, 5.0, 6.0] .+ c
        #= REPL[6]:6 =#
        return f(A, B) / c
    end
end

julia> dump(ex)
Expr
  head: Symbol block
  args: Array{Any}((2,))
    1: LineNumberNode
      line: Int64 2
      file: Symbol REPL[6]
    2: Expr
.
.
.
1 Like