Deep Dives
Core concepts and design decisions.
Documentation Structure
The adapt Primitive Why a single four-argument combinator is sufficient to implement every lens, prism, traversal, and parser in Bend.
Parse, Don't Validate How structured error returns replace boolean validation and carry proof of success.
Bidirectional Lenses Understanding read-write duality: get parses; set reconstructs through the same path.
Validation is Parsing Unifying schema validation, data parsing, and error recovery under one lens composition.
Guides
Section titled “Guides”How-To Guides
Step-by-step walkthroughs and practical examples.
Introduction to Lenses Hands-on introduction to building and composing lenses from simple operations.
Parsing with Bend From schema definition to full JSON parsing with error recovery and cardinality validation.
Working with Optics Isomorphisms, prisms, and traversals — beyond simple attribute access.
Reference
Section titled “Reference”API Documentation
Complete function reference and type documentation.
adapt — The Primitive Single four-argument combinator from which all Bend lenses compose.
Either right, left, mapR, mapL, chain, swap — proof types and operations.
Core Combinators identity, compose, pipe, parse, focus, iso, prism.
Bifunctors bimap, lmap, rmap — map success and failure branches.
Attributes & Paths attr, attrOr, path — focus on object keys and nested structures.
Type Parsers & Predicates int, str, bool, list, float, number, nonEmpty, nonBlank, optional, satisfy, andP, orP, notP, map.
Records & Validation record, recordAll, recordAllWith, defaultRecordError — schema validation.
Lists each, many, some, atLeast, exactly, index — apply lenses to list elements with cardinality control.
Collections eachValue, mapKey, sequence, zip — work with pairs, sequences, and object values.
Control Flow option, over, getOr, when, unless — conditional application and value extraction.
Error Recovery alt, choice, recover — fallback strategies and error handling.
Error Handling label, annotate, annotateWith, ensure, defaultPathError — wrap failures with context.
Function Application apply — extract named arguments from attrsets and call functions.
Debugging debug — trace lens activity to stderr.