kraken: csv: add writing functionality

Once again, pretty naive, but it will do.

src/csv/CMakeLists.txt

@@ -2,5 +2,7 @@ add_library(csv STATIC
   csv.hh
   read-csv.cc
   read-csv.hh
+  write-csv.cc
+  write-csv.hh
 )
 target_link_libraries(csv PRIVATE common_options)

src/csv/write-csv.cc

@@ -0,0 +1,16 @@
+#include "write-csv.hh"
+
+#include <algorithm>
+#include <iostream>
+#include <iterator>
+
+namespace kraken::csv {
+
+void write_csv(std::ostream& output, csv_type const& csv) {
+    for (const auto& line : csv) {
+        std::ranges::copy(line,
+                          std::ostream_iterator<std::string>{output, ","});
+    }
+}
+
+} // namespace kraken::csv

src/csv/write-csv.hh

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <iosfwd>
+#include <string>
+#include <vector>
+
+#include "csv/csv.hh"
+
+namespace kraken::csv {
+
+/// Write raw CSV data to an output-stream.
+void write_csv(std::ostream& output, csv_type const& csv);
+
+} // namespace kraken::csv