如何在 Nim 中将文件行作为参数传递？

Question

I'm learning Nim and I have a simple program that reads lines of a file. I would like to make it testable by extracting the main code in a function that takes an iterable of lines:

func countLines(lines: iterator): int =
  var n = 0
  for _ in lines:
    n += 1
  return n

if isMainModule:
    echo(countLines(lines "some_file.txt"))

The code above doesn't compile because of the following error: Error: attempting to call routine: 'lines' .

If I remove the superfluous code, I still get the same error:

echo(lines "some_file.txt")

Why can't I get the result of lines "some_file.txt" and pass it around? Is there some way to make this work?

Answer 1

This should be useful: https://nim-lang.org/docs/manual.html#iterators-and-the-for-statement-firstminusclass-iterators

We could create an intermediate iterator marked as closure that uses the inline lines :

iterator lines(f: string): string {.closure.} =
  for line in io.lines(f):
    yield line

func countLines(l: iterator(f: string): string, f: string): int =
  var n = 0
  for _ in ls(f):
    n += 1
  return n

when isMainModule:
  echo countLines(lines, "some_file.txt")

Nim allows you to write countLines in this way:

func countLines(l: iterator(f: string): string, f: string): int =
  for _ in ls(f):
    inc result

As result is auto-created and auto-returned.