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 (3 lines context)
to_unified_with(edits, old_name:, new_name:, context:)	Unified diff with custom context lines
to_ansi(edits, old_name:, new_name:)	Colored diff for terminal (red/green/cyan)
to_ansi_inline(edits)	Colored diff with bold changed characters
from_unified(input)	Parse unified diff into hunks
apply_patch(text, edits)	Apply edits to produce target text
apply_patch_fuzzy(text, edits, tolerance:)	Fuzzy patch (tolerates minor differences)

Merge

Function	Description
merge3(base, ours, theirs)	3-way merge with conflict detection

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,
  type MergeResult, MergeOk, MergeConflict,
  type Conflict, Conflict,
}

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
• context_lines.gleam — custom context line count
• ansi_output.gleam — colored terminal diff output
• fuzzy_patch.gleam — tolerant patch application
• merge3.gleam — 3-way merge with conflict handling

Development

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

License

MIT