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
DataFrame	Polars-backed tabular data (read, filter, aggregate, join, window functions, expressions, labels, recode)
DataFrame.Expr	Composable column expressions — arithmetic, comparisons, aggregations, date extractors, type casts, window functions
Date	Date operations (create, parse, format, compare, arithmetic)
DateTime	UTC-based date and time operations (parse, format, manipulate, Date/Time interop)
Decimal	Arbitrary-precision decimal arithmetic (rounding, parsing, conversion)
Distribution	Probability distributions (Normal, Uniform, Poisson, etc.) with sampling, PDF/CDF, and statistical moments
Duration	Time span operations (create, convert, arithmetic, comparison)
Http	HTTP client with composable request builders
IO	Input/output, files, and environment
Json	JSON parsing, encoding, and field extraction
List	List manipulation (map, filter, fold, etc.)
Math	Mathematical functions (abs, sqrt, sin, etc.)
Maybe	Composable optional handling (map, andThen, withDefault)
Num	Partition aggregate helpers for `windowMutate` closures (mean, sum, rank, denseRank, rowNumber, quantile, cumulative, rolling, lag/lead, first, last, count)
Regex	Compiled regular expression patterns (compile, test, find, replace, split, captures)
Result	Composable error handling (map, andThen, withDefault)
String	String operations (split, join, trim, etc.)
Table	Cross-tabulation and summary tables for statistical analysis
Time	Time-of-day operations (create, parse, format, compare, arithmetic)
ValueLabel	Access and transform individual ValueLabel pairs (value, label, create, map, match)
ValueLabelSet	Bidirectional Int↔String mappings for statistical value labels (supports `fromType` for compile-time extraction from ValueLabel enums)

Note: Keel also supports tasks for composing programs from multiple files at compile time. This is a language keyword using run "file" { ... } and task expecting/exposing declarations, 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

enum 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

enum 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

ValueLabel

enum ValueLabel = ValueLabel Int String

Carries an (Int, String) pair inside enum variants — the integer code and its human-readable label. Used for survey data, coded variables, and any domain where values have both numeric codes and descriptive names.

enum Gender
    = Male (ValueLabel 1 "Male")
    | Female (ValueLabel 2 "Female")

When you construct a ValueLabel variant (e.g., Gender::Male), the integer and label are auto-supplied from the type definition. See the types guide for details, ValueLabel for accessor and transform functions, and ValueLabelSet for extracting mappings at compile time.