Re: Download Pdf Reader
Joseph
Clojure is a homoiconic language, which is a fancy term describing the fact that Clojure programs are represented by Clojure data structures. This is a very important difference between Clojure (and Common Lisp) and most other programming languages - Clojure is defined in terms of the evaluation of data structures and not in terms of the syntax of character streams/files. It is quite common, and easy, for Clojure programs to manipulate, transform and produce other Clojure programs.
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.
'.' has special meaning - it can be used one or more times in the middle of a symbol to designate a fully-qualified class name, e.g. java.util.BitSet, or in namespace names. Symbols beginning or ending with '.' are reserved by Clojure. Symbols containing / or . are said to be 'qualified'.
Integers can be indefinitely long and will be read as Longs when in range and clojure.lang.BigInts otherwise. Integers with an N suffix are always read as BigInts. Octal notation is allowed with a 0 prefix, and hexadecimal notation is allowed with a 0x prefix. When possible, they can be specified in any base with radix from 2 to 36 (see Long.parseLong()); for example 2r101010, 052, 8r52, 0x2a, 36r16, and 42 are all the same Long.
Characters - preceded by a backslash: \c. \newline, \space, \tab, \formfeed, \backspace, and \return yield the corresponding characters. Unicode characters are represented with \uNNNN as in Java. Octals are represented with \oNNN.
Map literals can optionally specify a default namespace context for keys in the map using a #:ns prefix, where ns is the name of a namespace and the prefix precedes the opening brace { of the map. Additionally, #:: can be used to auto-resolve namespaces with the same semantics as auto-resolved keywords.
Keys that are keywords or symbols with a namespace are not affected except for the special namespace _, which is removed during read. This allows for the specification of keywords or symbols without namespaces as keys in a map literal with namespace syntax.
The keyed values in the map are assigned unevaluated to the relevant fields in the defrecord. Any defrecord fields without corresponding entries in the literal map are assigned nil as their value. Any extra keyed values in the map literal are added to the resulting defrecord instance.
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.
A shorthand version allows the metadata to be a simple symbol or string, in which case it is treated as a single entry map with a key of :tag and a value of the (resolved) symbol or string, e.g.:
^String x is the same as ^:tag java.lang.String x
Another shorthand version allows the metadata to be a keyword, in which case it is treated as a single entry map with a key of the keyword and a value of true, e.g.:
^:dynamic x is the same as ^:dynamic true x
A regex pattern is read and compiled at read time. The resulting object is of type java.util.regex.Pattern. Regex strings do not follow the same escape character rules as strings. Specifically, backslashes in the pattern are treated as themselves (and do not need to be escaped with an additional backslash). For example, (re-pattern "\\s*\\d+") can be written more concisely as #"\s*\d+".
For Symbols, syntax-quote resolves the symbol in the current context, yielding a fully-qualified symbol (i.e. namespace/name or fully.qualified.Classname). If a symbol is non-namespace-qualified and ends with '#', it is resolved to a generated symbol with the same name to which '_' and a unique id have been appended. e.g. x# will resolve to x_123. All references to that symbol within a syntax-quoted expression resolve to the same generated symbol.
For Lists/Vectors/Sets/Maps, syntax-quote establishes a template of the corresponding data structure. Within the template, unqualified forms behave as if recursively syntax-quoted, but forms can be exempted from such recursive quoting by qualifying them with unquote or unquote-splicing, in which case they will be treated as expressions and be replaced in the template by their value, or sequence of values, respectively.
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:
Clojure 1.7 introduced a new extension (.cljc) for portable files that can be loaded by multiple Clojure platforms. The primary mechanism for managing platform-specific code is to isolate that code into a minimal set of namespaces, and then provide platform-specific versions (.clj/.class or .cljs) of those namespaces.
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.
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Top and bottom reading
Endpoint and kinetic
Sequential multi-excitation
Sequential multi-emission
Simultaneous Dual Emission
Spectral scanning (absorbance)
Real-time ratiometric measurements
Well scanning
Optic Modules: Up to six application-specific modules (includes all filters, dichroics, etc. for an application)
For top and bottom reading
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Top and bottom reading
Endpoint and kinetic
Sequential multi-excitation
Sequential multi-emission
Spectral scanning (fluorescence, luminescence, absorbance)
Ratiometric measurements
Well scanning