tree_multiple_dispath.jl

using Test

abstract type AbstractNode end

struct FuncNode <: AbstractNode
    func::Function
    childlen::Vector{AbstractNode}
end

struct VarNode <: AbstractNode
    var::String
end

struct ConstNode <: AbstractNode
    value::Number
end

eval_tree(node::ConstNode, args) = node.value
eval_tree(node::VarNode,   args) = args[node.var]
eval_tree(node::FuncNode,  args) = node.func(eval_tree.(node.childlen, Ref(args)))

add(x) = x[1] + x[2]
sub(x) = x[1] - x[2]
mul(x) = x[1] * x[2]
div(x) = ifelse(x[2] == 0, 1, x[1] / x[2])

t = FuncNode(add, [
        FuncNode(mul, [
            ConstNode(5.0),
            VarNode("x")]),
         VarNode("y")])
args = Dict("x" => 2.0, "y" => 5.0)

@show eval_tree(t, args) # 15.0