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This method may block indefinitely reading from the reader, or writing to the writer. The behavior for the case where the reader and/or writer is asynchronously closed, or the thread interrupted during the transfer, is highly reader and writer specific, and therefore not specified.

If an I/O error occurs reading from the reader or writing to the writer, then it may do so after some characters have been read or written. Consequently the reader may not be at end of the stream and one, or both, streams may be in an inconsistent state. It is strongly recommended that both streams be promptly closed if an I/O error occurs.

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That said, most Clojure programs begin life as text files, and it is the task of the reader to parse the text and produce the data structure the compiler will see. This is not merely a phase of the compiler. The reader, and the Clojure data representations, have utility on their own in many of the same contexts one might use XML or JSON etc.

One might say the reader has syntax defined in terms of characters, and the Clojure language has syntax defined in terms of symbols, lists, vectors, maps etc. The reader is represented by the function read, which reads the next form (not character) from a stream, and returns the object represented by that form.

Since we have to start somewhere, this reference starts where evaluation starts, with the reader forms. This will inevitably entail talking about data structures whose descriptive details, and interpretation by the compiler, will follow.

The behavior of the reader is driven by a combination of built-in constructs and an extension system called the read table. Entries in the read table provide mappings from certain characters, called macro characters, to specific reading behavior, called reader macros. Unless indicated otherwise, macro characters cannot be used in user symbols.

Metadata is a map associated with some kinds of objects: Symbols, Lists, Vector, Sets, Maps, tagged literals returning an IMeta, and record, type, and constructor calls. The metadata reader macro first reads the metadata and attaches it to the next form read (see with-meta to attach meta to an object):

^{:a 1 :b 2} [1 2 3] yields the vector [1 2 3] with a metadata map of {:a 1 :b 2}.

The key in each pair is a tag that will be recognized by the Clojure reader. The value in the pair is the fully-qualified name of a Var which will be invoked by the reader to parse the form following the tag. For example, given the data_readers.clj file above, the Clojure reader would parse this form:

by invoking the Var #'my.project.foo/bar on the vector [1 2 3]. The data reader function is invoked on the form AFTER it has been read as a normal Clojure data structure by the reader. For your own data reader functions, you should report errors by throwing instances of RuntimeException with messages providing error information.

Reader tags without namespace qualifiers are reserved for Clojure. Default reader tags are defined in default-data-readers but may be overridden in data_readers.clj / data_readers.cljc or by rebinding *data-readers*. If no data reader is found for a tag, the function bound in *default-data-reader-fn* will be invoked with the tag and value to produce a value. If *default-data-reader-fn* is nil (the default), a RuntimeException will be thrown.

Clojure 1.4 introduced the instant and UUID tagged literals. Instants have the format #inst "yyyy-mm-ddThh:mm:ss.fff+hh:mm".NOTE: Some of the elements of this format are optional. See the code for details.The default reader will parse the supplied string into a java.util.Date by default. For example:

Since *data-readers* is a dynamic var that can be bound, you can replace the default reader with a different one. For example, clojure.instant/read-instant-calendar will parse the literal into a java.util.Calendar, while clojure.instant/read-instant-timestamp will parse it into a java.util.Timestamp:

If no data reader is found when reading a tagged literal, the *default-data-reader-fn* is invoked. You can set your own default data reader function and the provided tagged-literal function can be used to build an object that can store an unhandled literal. The object returned by tagged-literal supports keyword lookup of the :tag and :form:

In cases where is not feasible to isolate the varying parts of the code, or where the code is mostly portable with only small platform-specific parts, 1.7 also introduced reader conditionals, which are supported only in cljc files and at the default REPL. Reader conditionals should be used sparingly and only when necessary.

The syntax for #?@ is exactly the same but the expression is expected to return a collection that can be spliced into the surrounding context, similar to unquote-splicing in syntax quote. Use of reader conditional splicing at the top level is not supported and will throw an exception. An example:

The read and read-string functions optionally take a map of options as a first argument. The current feature set and reader conditional behavior can be set in the options map with these keys and values:

If the reader is invoked with {:read-cond :preserve}, the reader conditional and non-executed branches will be preserved, as data, in the returned form. The reader-conditional will be returned as a type that supports keyword retrieval for keys with :form and a :splicing? flag. Read but skipped tagged literals will be returned as a type that supports keyword retrieval for keys with :form and :tag keys.

An e-reader, also called an e-book reader or e-book device, is a mobile electronic device that is designed primarily for the purpose of reading digital e-books and periodicals.[1][2]

Any device that can display text on a screen may act as an e-reader; however, specialized e-reader devices may optimize portability, readability, and battery life for this purpose. Their main advantage over printed books is portability. This is because an e-reader is capable of holding thousands of books while weighing less than one book, and the convenience provided due to add-on features.[3][4]

Many e-readers can use the internet through Wi-Fi and the built-in software can provide a link to a digital Open Publication Distribution System (OPDS) library or an e-book retailer, allowing the user to buy, borrow, and receive digital e-books.[9] An e-reader may also download e-books from a computer or read them from a memory card.[10] However, the use of memory cards is decreasing as most of the 2010s era e-readers lack a card slot.[11]

An idea similar to that of an e-reader is described in a 1930 manifesto written by Bob Brown titled The Readies,[12] which describes "a simple reading machine which I can carry or move around, attach to any old electric light plug and read hundred-thousand-word novels in 10 minutes". His hypothetical machine would use a microfilm-style ribbon of miniaturized text which could be scrolled past a magnifying glass, and would allow the reader to adjust the type size. He envisioned that eventually words could be "recorded directly on the palpitating ether".[13]

The establishment of the E Ink Corporation in 1997 led to the development of electronic paper, a technology which allows a display screen to reflect light like ordinary paper without the need for a backlight. Among the first commercial e-readers were Sony's Data Discman (which was using Mini CDs with special caddies) and the Rocket eBook.[14] Several others were introduced around 1998, but did not gain widespread acceptance. Electronic paper was incorporated first into the Sony Librie that was released in 2004 and Sony Reader in 2006, followed by the Amazon Kindle, a device which, upon its release in 2007, sold out within five and a half hours.[15] The Kindle includes access to the Kindle Store for e-book sales and delivery.

As of 2009[update], new marketing models for e-books were being developed and a new generation of reading hardware was produced. E-books (as opposed to e-readers) had yet to achieve global distribution. In the United States, as of September 2009, the Amazon Kindle model and Sony's PRS-500 were the dominant e-reading devices.[16] By March 2010, some reported that the Barnes & Noble Nook may have been selling more units than the Kindle in the US.[17] The Ectaco jetBook Color was the first color e-reader on the market, but its muted colors were criticized.[18] As of 2021, a few color E-ink readers have been introduced into the market.[19]

Research released in March 2011 indicated that e-books and e-readers were more popular with the older generation than the younger generation in the UK. The survey, carried out by Silver Poll, found that around 6% of people over 55 owned an e-reader, compared with just 5% of 18- to 24-year-olds.[20] According to an IDC study from March 2011, sales for all e-readers worldwide rose to 12.8 million in 2010; 48% of them were Amazon Kindles, followed by Barnes & Noble Nooks, Pandigital, and Sony Readers (about 800,000 units for 2010).[21]

On January 27, 2010 Apple Inc. launched a multi-function tablet computer called the iPad[22] and announced agreements with five of the six largest publishers[23] that would allow Apple to distribute e-books.[24] The iPad includes a built-in app for e-book reading called iBooks and had the iBookstore for content sales and delivery. The iPad, the first commercially profitable tablet, was followed in 2011 by the release of the first Android-based tablets as well as LCD tablet versions of the Nook and Kindle. Unlike previous dedicated e-readers, tablet computers are multi-functional, utilize LCD touchscreen displays, and are more agnostic to e-book vendor apps, allowing for the installation of multiple e-book reading apps. Many Android tablets accept external media and allow uploading files directly onto the tablet's file system without resorting to online stores or cloud services. Many tablet-based and smartphone-based readers are capable of displaying PDF and DJVU files, which few of the dedicated e-book readers can handle. This opens a possibility to read publications originally published on paper and later scanned into a digital format. While these files may not be considered e-books in their strict sense, they preserve the original look of printed editions. The growth in general-purpose tablet use allowed for further growth in the popularity of e-books in the 2010s. ff782bc1db