Documentation

The readFile function reads a file and returns the contents of the file as a string. The file is read lazily, on demand, as with getContents.

The computation writeFile file str function writes the string str, to the file file.

The computation appendFile file str function appends the string str, to the file file.

Note that writeFile and appendFile write a literal string to a file. To write a value of any printable type, as with print, use the show function to convert the value to a string first.

main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])

The getContents operation returns all user input as a single string, which is read lazily as it is needed (same as hGetContents stdin).

Computation hGetContents hdl returns the list of characters corresponding to the unread portion of the channel or file managed by hdl, which is put into an intermediate state, semi-closed. In this state, hdl is effectively closed, but items are read from hdl on demand and accumulated in a special list returned by hGetContents hdl.

Any operation that fails because a handle is closed, also fails if a handle is semi-closed. The only exception is hClose. A semi-closed handle becomes closed:

• if hClose is applied to it;
• if an I/O error occurs when reading an item from the handle;
• or once the entire contents of the handle has been read.

Once a semi-closed handle becomes closed, the contents of the associated list becomes fixed. The contents of this final list is only partially specified: it will contain at least all the items of the stream that were evaluated prior to the handle becoming closed.

Any I/O errors encountered while a handle is semi-closed are simply discarded.

This operation may fail with:

• isEOFError if the end of file has been reached.

Write a string to the standard output device (same as hPutStr stdout).

The same as putStr, but adds a newline character.

Computation hPutStr hdl s writes the string s to the file or channel managed by hdl.

This operation may fail with:

• isFullError if the device is full; or
• isPermissionError if another system resource limit would be exceeded.

The same as hPutStr, but adds a newline character.

A string received from or being passed to the operating system, such as a file path, command-line argument, or environment variable name or value. With GHC versions before 7.2 on some platforms (posix) these are typically encoded. When converting, we assume the encoding is UTF-8 (cf http://www.dwheeler.com/essays/fixing-unix-linux-filenames.html#UTF8).

Convert a system string to an ordinary string, decoding from UTF-8 if it appears to be UTF8-encoded and GHC version is less than 7.2.

Convert a unicode string to a system string, encoding with UTF-8 if we are on a posix platform with GHC < 7.2.

A SystemString-aware version of error.

A SystemString-aware version of userError.

A SystemString-aware version of error that adds a usage hint.