Question

How can I access the abstract syntax tree for a generic function in Julia?

Answer 1

To recap: It looks like Simon was looking for the AST for a specific method associated with a generic function. We can get a LambdaStaticData object, which contains the AST, for a specific method as follows:

julia> f(x,y)=x+y

julia> f0 = methods(f, (Any, Any))[1]
((Any,Any),(),AST(:($(expr(:lambda, {x, y}, {{}, {{x, Any, 0}, {y, Any, 0}}, {}}, quote  # none, line 1:
        return +(x,y)
    end)))),())

julia> f0[3]
AST(:($(expr(:lambda, {x, y}, {{}, {{x, Any, 0}, {y, Any, 0}}, {}}, quote  # none, line 1:
        return +(x,y)
    end))))

julia> typeof(ans)
LambdaStaticData

Apparently this AST can either be an Expr object or a compressed AST object, represented as a sequence of bytes:

julia> typeof(f0[3].ast)
Array{Uint8,1}

The show() method for LambdaStaticData from base/show.jl illustrates how to decompress this, when encountered:

julia> ccall(:jl_uncompress_ast, Any, (Any, Any), f0[3], f0[3].ast)
:($(expr(:lambda, {x, y}, {{}, {{x, Any, 0}, {y, Any, 0}}, {}}, quote  # none, line 1:
        return +(x,y)
    end)))

julia> typeof(ans)
Expr