test.nim

import macros

macro callFilter(filter: stmt, value: stmt): expr =
    if value.kind == nnkStrLit:
        newStmtList(
            newNimNode(nnkConstSection).add(newNimNode(nnkConstDef).add(newIdentNode("filtered"), newEmptyNode(),
                       newCall(filter, value))),
            newIdentNode("filtered"))
    else:
        newCall(filter, value)

proc filterStuff(bla: string): string =
    "dummyFilter: " & bla


echo callFilter(filterStuff, "test1")

let test2 = "test2"
echo callFilter(filterStuff, test2)