Files

std.files is a thin layer over the host's file services. Everything that touches a file says !, because the world decides whether a read or a write lands.

main.luc

import std.files

func main() -> !:
    try files.write("notes.txt", "fig\npear\nplum\n")

    let whole = try files.read("notes.txt")
    print(f"{len(whole)} bytes")

    let lines = try files.read_lines("notes.txt")
    print(f"{len(lines)} lines")
    for index, line in lines:
        print(f"  {index}: {line}")

    var kept: List(String) = []
    for line in lines:
        if line != "pear":
            kept.append(line)
    try files.write_lines("kept.txt", kept)
    print(f"kept {len(try files.read_lines("kept.txt"))} lines")

Output

14 bytes
3 lines
  0: fig
  1: pear
  2: plum
kept 2 lines

read_lines strips newlines and adds no phantom empty line for a trailing one. write_lines joins with newlines, ends with one, and writes an empty file for an empty list.

Handling the failure#

main.luc

import std.files

func main():
    let text = files.read("does-not-exist.txt") catch "(nothing there)"
    print(text)

    files.write("/nowhere/at/all/x.txt", "data") catch:
        print("could not write outside the sandbox")

    print(f"exists: {files.exists("does-not-exist.txt")}")

Output

(nothing there)
could not write outside the sandbox
exists: false

exists answers a plain Bool and is the one call here that is not fallible — but it is a question about the past, never a guard for the call after it. There is a window between the two that nothing can close, and a guard could not tell "not there" from "would not open" anyway. Read the file and handle what the read says.

A word count#

Reading, splitting, counting and sorting, with the failure carried to the top by try.

input.txt

the quick brown fox
jumps over the lazy dog
the fox and the dog

main.luc

import std.files
import std.strings

func main() -> !:
    if arg_count() == 0:
        print("usage: wc FILE")
        return

    let path = arg(0)
    let text = try files.read(path)

    var counts = new Map(String, Int)
    for line in text.split("\n"):
        for word in line.split(""):
            counts[word] = counts.get(word, 0) + 1

    print(f"{len(counts)} distinct words in {path}")
    for word, seen in counts:
        if seen > 1:
            print(f"  {seen}  {word}")

Output

9 distinct words in input.txt
  4  the
  2  fox
  2  dog