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 test suite built from over a hundred English homophone pairs.

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✨ Features

• ✅ Returns primary and secondary phonetic keys for each word
• ✅ Behavior verified against canonical Double Metaphone test data
• ✅ Full FiveAM regression suite
• ✅ No external dependencies—just ANSI Common Lisp
• ✅ Licensed under Apache 2.0

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὎6 Installation

Clone or download the repository and load it with ASDF:

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

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ᾞ0 Usage

1. double-metaphone

Returns two values — the primary and secondary phonetic encodings for the given word.

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.

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2. metaphone-primary

Convenience wrapper that returns only the primary encoding.

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

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3. metaphone-alternate

Returns the secondary (alternate) encoding, when applicable.

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”.

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ᾞA Running the Tests

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")

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

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ὍC License

Apache 2.0

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ᾑ6 Disclaimer

This README was written with the assistance of ChatGPT.