Using lazy code to process large files

[Martin Drašar via Digitalmars-d-learn]

Hi,

I am struggling to use a lazy range-based code to process large text
files. My task is simple, i.e., I can write a non-range-based code in a
really short time, but I wanted to try different approach and I am
hitting a wall after wall.

Task: read a csv-like input, take only lines starting with some string,
split by a comma, remove leading and trailing whitespaces from splitted
elements, join by comma again and write to an output.

My attempt so far:

alias stringStripLeft = std.string.stripLeft;

auto input  = File("input.csv");
auto output = File("output.csv");

auto result = input.byLine()
                   .filter!(a => a.startsWith("..."))
                   .map!(a => a.splitter(","))
                   .stringStripleft // <-- errors start here
                   .join(",");

output.write(result);

Needless to say, this does not compile. Basically, I don't know how to
feed MapResults to splitter and then sensibly join it.

Thank you for any hint.
Martin