Reading Files in Miranda

Our first program will demonstrate reading files. Here’s the full source code:

|| Reading and writing files are basic tasks needed for
|| many Miranda programs. First we'll look at some examples of
|| reading files.

|| Reading files requires checking most operations for errors.
|| This helper will streamline our error checks below.
check_error :: (*) -> [char] -> *
check_error result error_msg
  = result, if result ~= error
  = error error_msg, otherwise

|| Main function to demonstrate file reading
main = 
  || Read entire file contents into memory
  let dat = check_error (readfile "/tmp/dat") "Error reading file"
  in (putstr dat) $

  || Open file for more controlled reading
  let f = check_error (openin "/tmp/dat") "Error opening file"
  in 

  || Read some bytes from the beginning of the file
  let b1 = take 5 (hd (lines f))
  in (putstr ("5 bytes: " ++ b1 ++ "\n")) $

  || Seek to a known location in the file and read from there
  let seek_pos = 6
  in let b2 = drop seek_pos (hd (lines f))
  in (putstr (show (length b2) ++ " bytes @ " ++ show seek_pos ++ ": " ++ take 2 b2 ++ "\n")) $

  || The Miranda standard library doesn't provide direct file seeking,
  || so we'll simulate it by reading and discarding characters

  || Read a specific number of bytes using a helper function
  let read_n_bytes n = take n (hd (lines f))
  in let b3 = read_n_bytes 2
  in (putstr (show (length b3) ++ " bytes: " ++ b3 ++ "\n")) $

  || Close the file when done
  closein f

|| Helper function to read a file and return its contents as a string
readfile :: [char] -> *
readfile filename = implode (hd (lines (openin filename)))

To run the program, save the code in a file with a .m extension (e.g., reading_files.m) and use the Miranda interpreter:

$ echo "hello" > /tmp/dat
$ echo "miranda" >> /tmp/dat
$ miranda reading_files.m
hello
miranda
5 bytes: hello
2 bytes @ 6: mi
2 bytes: he

Note that Miranda doesn’t have built-in functions for all the file operations we demonstrated in the original example. We’ve simulated some behaviors and simplified others to fit within Miranda’s capabilities. The core concepts of reading entire files, reading portions of files, and working with file handles are still demonstrated.

Miranda’s standard library is more limited compared to some modern languages, so advanced file manipulations might require additional custom functions or external libraries.

Next, we’ll look at writing files.

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Reading Files in Miranda