Demo/test of Nim macros

macro_demo.nim

import std/macros

macro makeVar(arg: varargs[untyped]): untyped =
    result = newStmtList()
    for a in arg:
        result.add newVarStmt(a, a)
    # echo result.treeRepr

macro lazyVar(arg: untyped): untyped =
    var statements = newStmtList()
    let fparms = arg.findChild(it.kind == nnkFormalParams)
    for fp in fparms: 
        if fp.kind == nnkIdentDefs:
            let vtype = fp[^2]
            if vtype.kind == nnkVarTy:
                # Operate only on constants
                continue
            if $vtype == "int":
                for v in fp:
                    if v.kind == nnkIdent:
                        if v == vtype:
                            break
                        statements.add newVarStmt(v, v)
    statements.add arg.body
    arg.body = statements
    return arg

proc add(a, b, c: int): int {.lazyVar.} =
    c = c + a + b
    return c

echo add(5, 4, 3)