File I/O

SCL provides several modules for reading and writing files. All file operations carry the <Proc> effect.

StringIO — line-by-line text files

StringIO is the simplest module for reading and writing text files line by line:

import "StringIO"

// Read all lines of a file into a list of strings
lines :: <Proc> [String]
lines = readLines "c:/data/input.txt"

// Write a list of strings to a file (one string per line)
writeLines "c:/data/output.txt" ["line 1", "line 2", "line 3"]

// Append lines to an existing file
appendLines "c:/data/log.txt" ["new entry"]

File — basic file operations

The File module provides general file and directory operations using a File data type:

import "File"

// Create a File reference
f = file "c:/data/report.txt"

// Test existence
if fileExists f
then print "exists"
else print "not found"

// Read entire file as a string
content = readFile f

// Write a string to a file (overwrites)
writeFile f "Hello, world!\n"

// Copy and move
copyFile f (file "c:/backup/report.txt")
moveFile f (file "c:/archive/report.txt")

// Delete
deleteFile f

// List directory contents
entries = listDirectory (file "c:/data")

Files — advanced path-based operations

The Files module is a more comprehensive alternative that uses a Path data type (backed by java.nio.file.Path):

import "Files"

p = path "c:/data/report.txt"

content = readTextFile p
writeTextFile p "Hello"
exists = pathExists p
allFiles = walkFileTree (path "c:/data")

Path supports relative paths, path composition with /, and platform-agnostic separator handling.

Stream — binary I/O

The Stream module exposes InputStream and OutputStream for binary data:

import "Stream"

// Open an input stream from a file
withInputStream "c:/data/binary.bin" $ \is ->
    // read bytes from is
    ...

// Open an output stream to a file
withOutputStream "c:/data/out.bin" $ \os ->
    // write bytes to os
    ...

Use Stream when you need byte-level control or when working with non-text files.

Serialization — binary object I/O

The Serialization module supports reading and writing SCL values as binary data via streams:

import "Serialization"

// Write a value to a stream
serialize outputStream myValue

// Read a value back from a stream
myValue = deserialize inputStream

The binary format is specific to SCL's serialization protocol; it is not interchangeable with Java serialization by default.

Path separator notes

On Windows, \ is the native path separator, but it is also the escape character in SCL strings. Use one of these forms:

"c:/data/file.txt"      // forward slashes work on all platforms
"c:\\data\\file.txt"    // escaped backslashes
"""c:\data\file.txt"""  // triple-quoted strings: no escape processing