Cli

The Cli module provides values-first command-line parsing helpers. It parses an explicit argument list with explicit specs and returns Result values. It does not read environment variables, inspect files, print help, or exit the process.

Pure Parser

Use Cli when application code should own argument sources, output, and error handling instead of delegating those effects to a parser.

Types

CliValueKind

CliStringKind | CliIntKind | CliBoolKind

Describes how a flag, option, or positional value should be parsed.

CliValue

CliString String | CliInt Int | CliBool Bool

The parsed value representation stored in ParsedOptions.values.

CliError

Structured errors returned by parsing functions.

Spec Builders

Cli.flag

String -> String -> CliSpec

Declare a boolean flag parsed from --name.

Cli.option

String -> CliValueKind -> Option CliValue -> String -> CliSpec

Declare a named option parsed from --name value or --name=value.

Cli.arg

NonNegativeInt -> String -> CliValueKind -> Bool -> Option CliValue -> String -> CliSpec

Declare a positional argument by zero-based index.

Cli.command

String -> String -> List CliSpec -> CliCommandSpec

Declare a top-level subcommand and its option specs.

Parsing

Cli.parse

List String -> List CliSpec -> Result ParsedOptions CliError

Parse flags, options, and positional arguments from an argument list.

specs = [
  Cli.flag "verbose" "Enable verbose output",
  Cli.option "limit" CliIntKind (Some (CliInt 10)) "Maximum rows",
  Cli.arg 0 "input" CliStringKind true None "Input file"
]

parsed = Cli.parse ["--verbose", "--limit=25", "data.csv"] specs

Cli.parse-command

List String -> List CliCommandSpec -> Result ParsedCommand CliError

Parse a top-level subcommand and then parse that command's options.

Usage Text

Cli.usage

String -> List CliSpec -> String

Generate usage text from option declarations in declaration order.

Cli.command-usage

String -> List CliCommandSpec -> String

Generate command usage text from command declarations in declaration order.