I/O & Environment

Functions for file operations and environment variable access.

File Operations

read_file

Signature: read_file(path: String) -> String

Reads the entire contents of a file as a string.

fn main() -> Unit using file_io
  content = read_file("example.txt")
  print(content)
end fn

Notes:

• The path can be absolute or relative to the current working directory
• Throws an error if the file does not exist or cannot be read
• Returns the entire file content as a single string

write_file

Signature: write_file(path: String, content: String) -> Unit

Writes a string to a file, creating the file if it doesn't exist or overwriting if it does.

fn main() -> Unit using file_io
  write_file("output.txt", "Hello, Kettle!")
  print("File written")
end fn

Notes:

• Creates parent directories if they don't exist
• Completely overwrites existing file content
• Returns Unit on success, throws error on failure

file_exists

Signature: file_exists(path: String) -> Bool

Checks whether a file exists at the given path.

fn main() -> Unit using file_io
  match file_exists("config.json")
    True -> print("Config found")
    False -> print("No config")
  end match
end fn

Notes:

• Returns true if the file exists and is readable
• Returns false if the file doesn't exist or is not accessible

Environment

get_env

Signature: get_env(name: String) -> String

Retrieves the value of an environment variable.

fn main() -> Unit using file_io
  home = get_env("HOME")
  print("Home: \${home}")
end fn

Notes:

• Returns an empty string if the variable is not set
• Variable names are case-sensitive on Unix systems

Common Patterns

Copying Files

Processing File Lines

Configuration with Fallback

Error Handling

File operations can fail for various reasons (file not found, permission denied, etc.). Currently, these operations will cause a runtime error. For safer handling:

fn safe_read(path: String) -> Option[String] with IO
  match file_exists(path)
    True -> Some(read_file(path))
    False -> None
  end match
end fn

fn main() -> Unit using file_io
  match safe_read("maybe.txt")
    Some(content) -> print(content)
    None -> print("File not found")
  end match
end fn

Function Summary

Function	Signature	Description
read_file	String -> String	Read file contents
write_file	(String, String) -> Unit	Write string to file
file_exists	String -> Bool	Check if file exists
get_env	String -> String	Get environment variable

See Also

• Types & Conversions - String operations for processing file content
• Lists - Working with lines and data
• Quantum Operations - Quantum computing functions