Hi everybody, I was doing an assignment in Java for my university concerning a program that reads, modifies and writes CSV files, when I suddenly had the idea of implementing parts of this in Haskell for fun. When I finished the Haskell programm, I was disappointed by the performance: To parse a 200k lines CSV file, insert a line (yes I know i could insert a line without parsing the file, that's just an example) at pos. 199999 and write the file again, the Java program takes 1.1 seconds while the Haskell program takes 12.5 seconds. I have read Don's blog post but am unsure how to implement his tips into my program, as I am still kind of a Haskell beginner. The source code (40 lines incl. comments and empty lines) and the 200k CSV file I used for testing and a smaller CSV file demonstrating the special easy-to-parse CSV syntax are available on my ftp server, ftp://baah.servegame.org/public/haskell The call syntax is <program> <csv file> <line to insert> e.g. main lang.csv "test","this","line" I haven't posted the source code here directly because I thought it might be too long. If someone here finds the time to look at my code and give me some hints, that would really be nice. Regards Philip