gliff

A text diffing library for Gleam.

Myers diff, patience diff, unified diff format, patch application, semantic cleanup, and inline highlighting.

Installation

gleam add gliff

Quick Start

import gliff
import gliff/types.{Delete, Equal, Insert}

pub fn main() {
  let old = "hello\nworld"
  let new = "hello\ngleam"

  let edits = gliff.diff(old, new)
  // [Equal(["hello"]), Delete(["world"]), Insert(["gleam"])]

  let unified = gliff.to_unified(edits, old_name: "a.txt", new_name: "b.txt")
  // "--- a.txt\n+++ b.txt\n@@ -1,2 +1,2 @@\n hello\n-world\n+gleam\n"

  let assert Ok(result) = gliff.apply_patch(old, edits)
  // "hello\ngleam"
}

API

Diffing

Function	Description
`diff(old, new)`	Line-level diff (Myers)
`diff_chars(old, new)`	Character-level diff
`diff_words(old, new)`	Word-level diff
`diff_myers(old, new)`	Explicit Myers algorithm
`diff_patience(old, new)`	Patience algorithm (anchors on unique lines)
`diff_with(old, new, config)`	Configurable: algorithm + cleanup + budget
`diff_chars_with(old, new, config)`	Character-level with config
`default_config()`	`DiffConfig(Myers, NoCleanup, 0)`

Output & Patching

Function	Description
`to_unified(edits, old_name:, new_name:)`	Format as unified diff string
`from_unified(input)`	Parse unified diff into hunks
`apply_patch(text, edits)`	Apply edits to produce target text

Post-Processing

Function	Description
`cleanup_semantic(edits)`	Eliminate trivial equalities, merge edits
`cleanup_semantic_lossless(edits)`	Shift edits to natural boundaries
`similarity(edits)`	Ratio from 0.0 (different) to 1.0 (identical)
`inline_highlight(edits)`	Character-level spans within changed lines

Types

All types live in gliff/types:

import gliff/types.{
  type Edit, Equal, Insert, Delete,
  type Hunk, Hunk,
  type InlineEdit, InlineEqual, InlineDelete, InlineInsert,
  type Span, Changed, Unchanged,
  type DiffConfig, DiffConfig,
  type Algorithm, Myers, Patience,
  type Cleanup, NoCleanup, SemanticCleanup, SemanticLosslessCleanup,
  type DiffResult, Complete, Truncated,
}

Examples

See examples/ for runnable code with annotated output:

basic.gleam — diff, unified output, patch, similarity
word_diff.gleam — word-level diffing
patience_diff.gleam — Myers vs Patience comparison
inline_highlight.gleam — character-level change spans
configurable.gleam — algorithm, cleanup, and budget config

Development

gleam test                     # Erlang
gleam test --target javascript # JavaScript

License

MIT