Common Lisp implementation of the Double Metaphone phonetic algorithm.

cl-double-metaphone

# cl-double-metaphone

A pure Common Lisp implementation of **Lawrence Philips’ Double Metaphone** phonetic encoding algorithm.

Double Metaphone is a refinement of the classic Metaphone algorithm for English.  
It encodes words into short letter sequences that represent how they sound rather than how they’re spelled.  
This makes it useful for:

- Fuzzy text matching (e.g., “Smith” ≈ “Smyth”)
- Deduplication and record linkage
- Search engines and spell-checkers
- Linguistic or genealogy research

This implementation aims for **complete compatibility** with the reference C version, verified through a
comprehensive [FiveAM](https://github.com/sionescu/fiveam) test suite built from over a hundred English
homophone pairs.

---

## ✨ Features

- ✅ Returns **primary** and **secondary** phonetic keys for each word  
- ✅ Behavior verified against canonical Double Metaphone test data  
- ✅ Full [FiveAM](https://github.com/sionescu/fiveam) regression suite  
- ✅ No external dependencies—just ANSI Common Lisp  
- ✅ Licensed under Apache 2.0

---

## ὎6 Installation

Clone or download the repository and load it with ASDF:

```lisp
(ql:quickload "cl-double-metaphone")
```

---

## ᾞ0 Usage

### 1. `double-metaphone`
Returns **two values** — the primary and secondary phonetic encodings for the given word.

```lisp
CL-USER> (multiple-value-list (double-metaphone:double-metaphone "Smith"))
("SM0" "XMT")

CL-USER> (multiple-value-list (double-metaphone:double-metaphone "Schmidt"))
("XMT" "SMT")
```

If two words sound alike, their primary or secondary keys will usually match.

---

### 2. `metaphone-primary`
Convenience wrapper that returns **only** the primary encoding.

```lisp
CL-USER> (double-metaphone:metaphone-primary "Knight")
"NT"
```

---

### 3. `metaphone-alternate`
Returns the **secondary (alternate)** encoding, when applicable.

```lisp
CL-USER> (double-metaphone:metaphone-alternate "Knight")
"NT"
```

For many English words, both encodings are identical.  
Differences appear for ambiguous spellings such as “Smith”/“Schmidt” or “Steven”/“Stephen”.

---

## ᾞA Running the Tests

```lisp
CL-USER> (ql:quickload "cl-double-metaphone/tests")
To load "cl-double-metaphone/tests":
  Load 1 ASDF system:
    cl-double-metaphone/tests
; Loading "cl-double-metaphone/tests"

("cl-double-metaphone/tests")
```

```lisp
CL-USER> (asdf:test-system :cl-double-metaphone/tests)

Running test suite DOUBLE-METAPHONE-SUITE
 Running test BASIC-ENGLISH-NAMES .....
 Running test SIMILAR-SOUNDING-NAMES ..
 Running test EDGE-CASES ....
 Running test CAPITALIZATION ..
 Running test ENGLISH-HOMOPHONES ........[...]
 Did 149 checks.
    Pass: 149 (100%)
    Skip: 0 ( 0%)
    Fail: 0 ( 0%)

T
```

---

## ὍC License

Apache 2.0

---

## ᾑ6 Disclaimer

This README was written with the assistance of ChatGPT.


Implements Lawrence Philips’ Double Metaphone algorithm in pure Common Lisp.
   Returns primary and secondary phonetic keys for English words.  Useful for
   fuzzy matching, search indexing, and linguistic experiments.  Includes
   a complete FiveAM test suite.

fiveam

FiveAM test suite for cl-double-metaphone.

cl-double-metaphone

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