**So, first questions: What are streams, what are they used for?**
A `Stream` is an abstraction for anything that provide an input stream of
bytes. A stream of bytes is just a sequence of bytes, obtained one at a time.
On top of this, many operations can be implemented, such as reading full lines,
etc.
**So here is my second question: What is happening, and what can I do about
it?**
I'm not going to try to explain everything that's happening in your code but
instead provide you with a working (reduced) example of how I would go about
doing something similar to what you're doing, which is basically trying to pass
iterators to procs. (Hopefully I understood your need correctly.)
import os, streams, zip/gzipfiles
# Convert a stream into an iterator of lines
proc linesIterator(stream: Stream): iterator(): string =
result = iterator(): string =
while not stream.atEnd:
yield stream.readLine()
# Convert an iterator of strings into a seq of strings
# (contrived illustration of passing an iterator to a proc)
proc readAllLines(iter: iterator(): string): seq[string] =
result = newSeq[string]()
for line in iter():
result.add(line)
# Main code
if paramCount() < 1:
echo "Usage: stream_example [filename]"
quit(1)
let filename = paramStr(1)
let stream: Stream =
if filename[^3 .. ^1] == ".gz":
newGZFileStream(filename)
else:
newFileStream(filename, fmRead)
if stream == nil:
echo "Unable to open file: " & filename
quit(1)
let lines = linesIterator(stream)
let allLines = readAllLines(lines)
for line in allLines:
echo line
stream.close()
As you can see above, the `stream` can be either a `FileStream` or a
`GZipFileStream`, the rest of the program doesn't care because both are streams.
Note that the `linesIterator` proc _returns_ an iterator instead of being an
iterator itself. (It is a closure iterator because it captures variables from
the environment, namely the stream parameter but we don't have to explicitly
annotate this; Nim implicitly figures this out.)
PS: You'll need nimble to compile this program because of the dependency on the
zip package.
