File System & I/O

File and stream I/O in Wysna is designed around deterministic resource cleanup and explicit error handling with fallible channels (T ! E).

Reading and Writing Files (Prelude Built-ins)

Wysna includes first-class built-in functions in the prelude for common file operations without requiring module imports:

Reading Files

fn main() -> unit {
    let result = read_file("config.json") else err {
        print("Failed to read file:", err.message)
        return
    }

    print("File Content:")
    print(result)
}

Because reading can fail (e.g., file not found or permission denied), read_file returns str ! IoError.

Writing Files

To write UTF-8 text to a file on disk:

fn save_report(filename: str, content: str) -> unit ! IoError {
    write_file(filename, content)?
    print("Report saved successfully to:", filename)
}

fn main() -> unit {
    save_report("output.txt", "Wysna v0.5.0 compilation report\n") else err {
        print("Error saving report:", err.message)
    }
}

---

Filesystem Operations (std/fs)

For low-level filesystem manipulations (checking existence, creating directories, deleting or renaming files), import "std/fs.wysna":

import "std/fs.wysna"

fn main() -> unit {
    # Check if a path exists
    let is_present = fs.exists("data/cache") else err {
        false
    }

    if is_present {
        print("Cache directory exists")
    } else {
        fs.mkdir("data/cache") else err {
            print("Failed to create directory:", err.operation)
        }
    }
}

Available std/fs functions:

• fs.exists(path: str) -> bool ! FsError
• fs.size(path: str) -> int ! FsError
• fs.mkdir(path: str) -> unit ! FsError
• fs.remove(path: str) -> unit ! FsError
• fs.rename(path: str, target: str) -> unit ! FsError