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#lang scribble/manual
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@(require scribble/eval (for-label racket "../main.rkt"))
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@(define my-eval (make-base-eval))
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@(my-eval `(require "../main.rkt"))
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@title{Hyphenate}
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@author{Matthew Butterick (mb@"@"mbtype.com)}
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A simple hyphenation engine that uses the Knuth–Liang hyphenation algorithm originally developed for TeX. This implementation is a port of Ned Batchelder's @link["http://nedbatchelder.com/code/modules/hyphenate.html"]{Python version}. I can claim only the most inconsequential shred of authorial credit.
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I originally developed this module to handle hyphenation for my web-based book @link["http://practicaltypography.com"]{Butterick's Practical Typography}. Among web browsers, support for CSS-based hyphenation is still iffy, but soft hyphens work reliably well. Putting them into the text manually, however, is a drag. Hence @racketmodname[hyphenate].
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@defmodule[hyphenate]
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@defproc[
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(hyphenate
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[text string?]
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[joiner (or/c char? string?) (integer->char #x00AD)]
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[#:exceptions exceptions (listof string?) empty]
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[#:min-length length (or/c integer? false?) 5])
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string?]
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Hyphenate @racket[_text] by calculating hyphenation points and inserting @racket[_joiner] at those points. By default, @racket[_joiner] is the soft hyphen (Unicode 00AD = decimal 173). Words shorter than @racket[#:min-length] @racket[_length] will not be hyphenated. To hyphenate words of any length, use @racket[#:min-length] @racket[#f].
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@margin-note{The REPL displays a soft hyphen as \u00AD. But in ordinary use, you'll only see a soft hyphen when it appears at the end of a line or page as part of a hyphenated word. Otherwise it's not displayed. In most of the examples here, I use a standard hyphen for clarity.}
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@examples[#:eval my-eval
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(hyphenate "ergo polymorphic")
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(hyphenate "ergo polymorphic" #\-)
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(hyphenate "ergo polymorphic" #:min-length 13)
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(hyphenate "ergo polymorphic" #:min-length #f)
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]
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Because the hyphenation is based on an algorithm rather than a dictionary, it makes good guesses with unusual words:
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@examples[#:eval my-eval
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(hyphenate "scraunched strengths" #\-)
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(hyphenate "Racketcon" #\-)
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(hyphenate "supercalifragilisticexpialidocious" #\-)
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]
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Using the @racket[#:exceptions] keyword, you can pass hyphenation exceptions as a list of words with permissible hyphenation points marked with regular hyphen characters (@racket["-"]). If an exception word contains no hyphens, that word will never be hyphenated.
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@examples[#:eval my-eval
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(hyphenate "polymorphic" #\-)
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(hyphenate "polymorphic" #\- #:exceptions '("polymo-rphic"))
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(hyphenate "polymorphic" #\- #:exceptions '("polymorphic"))
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]
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Knuth & Liang were sufficiently confident about their algorithm that they originally released it with only 14 exceptions: @italic{associate[s], declination, obligatory, philanthropic, present[s], project[s], reciprocity, recognizance, reformation, retribution}, and @italic{table}. Admirable bravado, but it's not hard to discover others.
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@examples[#:eval my-eval
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(hyphenate "wrong: columns signage lawyers" #\-)
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(hyphenate "right: columns signage lawyers" #\-
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#:exceptions '("col-umns" "sign-age" "law-yers"))
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]
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Overall, my impression is that the Knuth–Liang algorithm tends to miss legitimate hyphenation points (i.e., it generates false negatives) more often than it creates erroneous hyphenation points (i.e., false positives). This is good policy. Perfect hyphenation — that is, hyphenation that represents an exact linguistic syllabification of each word — is hardly useful in typesetting contexts. Hyphenation simply seeks to mark possible line-break and page-break locations for whatever text-layout engine is drawing the text. A word wrongly hyphenated is more likely noticed by a reader than a word inefficiently hyphenated.
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For this reason, certain words can't be hyphenated algorithmically, because the correct hyphenation depends on meaning, not merely on spelling. For instance:
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@examples[#:eval my-eval
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(hyphenate "adder")
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]
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This is the right result. If you used @italic{adder} to mean the machine, it would be hyphenated @italic{add-er}; if you meant the snake, it would be @italic{ad-der}. Better to avoid hyphenation than to hyphenate incorrectly.
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Don't send raw HTML through @racket[hyphenate]. It can't distinguish HTML tags and attributes from textual content, so it will hyphenate everything, breaking your markup.
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@examples[#:eval my-eval
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(hyphenate "<body style=\"background: yellow\">Hello world</body>")
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]
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So pass your textual content through @racket[hyphenate] @italic{before} you put it into your HTML template. Or convert your HTML to an @tech{X-expression} and process it selectively (e.g., with @racket[match]).
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@defproc[
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(hyphenatef
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[text string?]
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[pred procedure?]
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[joiner (or/c char? string?) (integer->char \#x00AD)]
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[#:exceptions exceptions (listof string?) empty]
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[#:min-length length (or/c integer? false?) 5])
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string?]
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Like @racket[hyphenate], but only words matching @racket[_pred] are hyphenated. Convenient if you want to prevent hyphenation of certain sets of words, like proper names:
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@examples[#:eval my-eval
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(hyphenate "Brennan Huff likes fancy sauce" #\-)
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(define uncapitalized? (λ(word) (let ([letter (substring word 0 1)])
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(equal? letter (string-downcase letter)))))
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(hyphenatef "Brennan Huff likes fancy sauce" uncapitalized?
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#\-)
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]
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@defproc[
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(unhyphenate
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[text string?]
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[joiner (or/c char? string?) @(integer->char #x00AD)])
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string?]
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Remove @racket[_joiner] from @racket[_text] using @racket[string-replace].
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A side effect of using @racket[hyphenate] is that soft hyphens (or whatever the @racket[_joiner] is) will be embedded in the output text. If you need to support copying of text, for instance in a GUI application, you'll probably want to strip out the hyphenation before the copied text is moved to the clipboard.
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@examples[#:eval my-eval
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(hyphenate "ribbon-cutting ceremony")
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(unhyphenate (hyphenate "ribbon-cutting ceremony"))
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]
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Keep in mind that @racket[unhyphenate] won't produce the input originally passed to @racket[hyphenate] if @racket[_joiner] appeared in the original input.
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@examples[#:eval my-eval
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(hyphenate "ribbon-cutting ceremony" #\-)
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(unhyphenate (hyphenate "ribbon-cutting ceremony" #\-) #\-)
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]
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