playing with types and inheritance in nim-lang

nimtypes.nim

import strutils # provides parseInt for us

type
    Node = ref object of RootObj
        value: string
        active: bool

type
    NumNode = ref object of Node

type
    BinOp = ref object of Node
        left, right: Node
        op: string

var add = BinOp(
    left: NumNode(value: "7"),
    op: "+",
    right: NumNode(value: "9"),
    active: true
)

echo add[]
# > (left: ...right: ...op: "+", value: "", active: true)

var multiply = BinOp(
    left: add,
    op: "*",
    right: NumNode(value: "3"),
    active: true
)

echo multiply[]
# > (left: ...right: ...op: "*", value: "", active: true)

echo multiply[]
# > (left: ...right: ...op: "*", value: "", active: true)

proc interpret(node: Node): int =
    if node of NumNode:
        return parseInt(node.value)

    if node of BinOp:
        let n = BinOp(node)

        if n.op == "+":
            return interpret(n.left) + interpret(n.right)

        if n.op == "*":
            return interpret(n.left) * interpret(n.right)

echo interpret(multiply)