Standard Library

The Keel standard library provides essential modules for common programming tasks. Modules must be imported before use.

Importing Modules

-- Import specific functions
import List exposing (map, filter)

-- Or use qualified access
import List

List.map (|x| x * 2) [1, 2, 3]

Available Modules

Module	Description
List	List manipulation (map, filter, fold, etc.)
String	String operations (split, join, trim, etc.)
Math	Mathematical functions (abs, sqrt, sin, etc.)
Decimal	Arbitrary-precision decimal arithmetic (rounding, parsing, conversion)
IO	Input/output, files, and environment
Http	HTTP client with composable request builders
Json	JSON parsing, encoding, and field extraction
DataFrame	Polars-backed tabular data (read, filter, aggregate, join, window functions, expressions, labels, recode)
Table	Cross-tabulation and summary tables for statistical analysis
ValueLabelSet	Bidirectional Int↔String mappings for statistical value labels
Date	Date operations (create, parse, format, compare, arithmetic)
Time	Time-of-day operations (create, parse, format, compare, arithmetic)
Duration	Time span operations (create, convert, arithmetic, comparison)
DateTime	UTC-based date and time operations (parse, format, manipulate, Date/Time interop)
Result	Composable error handling (map, andThen, withDefault)
Maybe	Composable optional handling (map, andThen, withDefault)

Note: Keel also supports file inlining for composing programs from multiple files at compile time. This is a language feature using inline "file" passing (...), not a stdlib module.

Note: File system operations in the IO module, HTTP requests, and DataFrame file operations are disabled by default for security. See the IO Security Guide for configuration options.

Built-in Types

These types are always available without imports:

Maybe

type Maybe a = Just a | Nothing

Represents an optional value.

let present: Maybe Int = Just 42
let absent: Maybe Int = Nothing

case present of
    Just n -> n
    Nothing -> 0

Try it

Result

type Result a e = Ok a | Err e

Represents success or failure.

let success: Result Int String = Ok 42
let failure: Result Int String = Err "not found"

case success of
    Ok n -> n
    Err msg -> 0