hmm.nim

import os, streams, parsexml, strutils, macros

macro readModelAndBuildAST(filename: string): stmt =
    let
        inputString = slurp(filename.strVal)

    var s = newStringStream(inputString)
    var x: XmlParser
    open(x, s, filename)

    next(x)
    while true:
        case x.kind
        of xmlEof: break
        of xmlElementOpen, xmlElementStart:
            case x.elementName
            of "constant":
                x.next
                echo x.attrKey
                echo x.attrValue
                x.next
                echo x.attrKey
                echo x.attrValue
            else: discard
        else: discard
        next(x)

output.txt

parse.nim(9, 9) Error: type mismatch: got (XmlParser, StringStream, NimNode)
but expected one of: 
system.open(f: var File, filename: string, mode: FileMode, bufSize: int)
parsexml.open(my: var XmlParser, input: Stream, filename: string, options: set[XmlParseOption])
system.open(f: var File, filehandle: FileHandle, mode: FileMo