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Milan Kemezy
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.
Library of Congress registered readers may use the Library of Congress Online Catalog to request materials from the Library's general collections, the Law Library, and from the Asian and Music Division collections. The automated call slip service (ACS) offers delivery of materials only to the Library's Main, Science and Business, European, Hispanic, Law, and Performing Arts reading rooms.
All U.S. citizens, or persons legally residing in the U.S. who are blind or visually impaired can request a free currency reader from the Bureau of Engraving and Printing by downloading the application below. The application is provided in both English and Spanish. The application must be filled out completely, signed by a competent authority who can certify eligibility, and returned to the mailing address provided on the form.
We have spent over 15 years developing the global solution: a free, high quality screen reader, accessible to all! NVDA: Non-Visual Desktop Access.We have already enabled 200,000+ people to gain freedom, education and employment!
On this page you can find links to accessibility help articles that are written for people who use screen readers with Microsoft Word. To find information on how to create Word documents that are accessible to people with disabilities, see Make your Word documents accessible to people with disabilities.
Write implements the standard Write interface:it writes data to the pipe, blocking until one or more readershave consumed all the data or the read end is closed.If the read end is closed with an error, that err isreturned as err; otherwise err is ErrClosedPipe.
MultiReader returns a Reader that's the logical concatenation ofthe provided input readers. They're read sequentially. Once allinputs have returned EOF, Read will return EOF. If any of the readersreturn a non-nil, non-EOF error, Read will return that error.
When we started planning Summer Reading, we were still in Covid-19 lockdown mode. Reader Zone had features we appreciated. That it was affordable was icing on the cake!
Our experiment with Reader Zone was successful. We extended our subscription to add more challenges and contests for readers of all ages.
We introduced the app to our patrons on social media and through our paper Summer Reading information. We also created a short video to explain how to sign into the app and use its features. We wanted to make this as simple and stress-free as possible, and this helped to flatten out the learning curve. Once they got the hang of it, our community really took to it! We saw an almost 50% increase in the number of adults participating in Summer Reading, and for kids, we saw an uptick in completion rates. Overall, we felt that our Summer Reading experiment with Reader Zone was successful, and we extended our subscription to add more challenges and contests for readers of all ages through the next year.
Introducing Thorium, a new free desktop EPUB reader for Windows and Mac, 24th Annual Accessing Higher Ground, November 2019, speakers Richard Orme (CEO) and George Kerscher (Chief Innovations Officer), DAISY Consortium.
A reader who fails the retest must take it again and pass before the end of their five-year approval period expires in order retain their B Reader status. There is no waiting period between failing the retest and taking it again. B Readers who do not retest and pass before their expiration date will lose their certification and will not be able to provide B readings until they pass the exam.
A reader account enables data consumers to access and query data shared by the provider of the account, with no setup or usage costs forthe consumer, and no requirements for the consumer to sign a licensing agreement with Snowflake.
The reader account is created, owned, and managed by the provider account, which assumes all responsibility for credit charges incurred byusers in the reader account. Similar to standard consumer accounts, the provider account uses shares to share databases with readeraccounts; however, a reader account can only consume data from the provider account that created it.
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