Language Guide

This guide covers the core concepts and features of the Keel programming language.

Fundamentals

• Basics — Values, types, comments, and core language concepts
• Variables — Declaring variables, type annotations, shadowing, and destructuring
• Operators — Arithmetic, comparison, logical, string, list, and pipe operators
• Functions — Defining functions, type signatures, higher-order functions, lambdas, and currying
• Control Flow — If expressions, case expressions, and pattern-based branching

Data Structures

• Types — Type aliases, enums, generics, records, and type inference
• Collections — Lists, tuples, records, and common operations
• Pattern Matching — Literals, constructors, guards, as-patterns, and exhaustiveness
• Modules — Inline modules, file modules, imports, aliases, and exports
• Error Handling — Understanding Keel's error messages and common mistakes

Code Structure

• Indentation and Scope — How indentation controls code structure, multiline arguments, and scoping rules

Data Science

• Temporal Types — Date, Time, DateTime, and Duration types
• DataFrame Expressions — Composable column expressions for efficient DataFrame operations
• DataFrame Type Safety — Schema annotations, column type checking, and compile-time performance
• Data Contracts — Compile-time validation of DataFrame column values
• Data Lineage — Track data provenance and transformation history
• DataFrame Reshaping — Reshape wide data to long format with melt
• Matrices — Matrix creation, arithmetic, decompositions, and DataFrame interop

Projects

• Tasks — Composing programs from multiple files with compile-time task execution
• Projects — Organizing code with manifests and permissions

Tooling

• Tracing and Debugging — Inspecting compilation and execution with keel trace