Blorp by Example

Building a Small CLI App

Keep parsing and I/O at the edge, with a pure core that is easy to test.

Argparse

std/argparse provides a Cli record plus flag, option, parse, and accessor helpers.

argparse.brp

cli: Cli = { name = "app", version = "0.1", description = "demo", params = [] }

Pure Core

Put deterministic word-count logic in pure functions.

core.brp

pure func count_words(text: String) -> Int:
    text.words().length()

Impure Shell

Read files, parse args, and print in main.

shell.brp

func main(args: List[String]) -> Int:
    print(count_words("one two").to_string())
    0

Tests

Test the pure core without invoking the CLI.

test.brp

func test_count_words() -> Bool:
    count_words("one two") == 2

Example

wordcount.brp

import:
	argparse:
		Cli,
		ParseOutcome(Parsed, HelpRequested, VersionRequested, ParseFailed),
		format_error,
		get_int_or,
		option_int,
		parse,


pure func count_words(text: String, min_len: Int) -> Int:
	var count: Int = 0
	for word in text.words():
		if word.length() >= min_len:
			count += 1
	count


func main(args: List[String]) -> Int:
	cli: Cli = {
		name = "wordcount",
		version = "0.1",
		description = "count words",
		params = [option_int("min-length", "--min-length", "-m", "minimum length", "N")],
	}
	match parse(cli, args):
		Parsed(parsed):
			min_len: Int = get_int_or(parsed, "min-length", 1)
			print(count_words("one three seven", min_len).to_string())
			0
		ParseFailed(err):
			eprintln(format_error(err))
			1
		HelpRequested(text):
			print(text)
			0
		VersionRequested(text):
			print(text)
			0

Try It

terminal

blorp run wordcount.brp -- --min-length 4