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The observer design pattern is a behavioural pattern listed among the 23 well-known "Gang of Four" design patterns that address recurring design challenges in order to design flexible and reusable object-oriented software, yielding objects that are easier to implement, change, test and reuse.
When REGEXP matches the input string, control flow is transferred to the associated CODE. There is one special rule: the default rule with * instead of REGEXP ; it is triggered if no other rules matches. re2c has greedy matching semantics: if multiple rules match, the rule that matches longer prefix is preferred; if the conflicting rules match ...
The raw input, the 43 characters, must be explicitly split into the 9 tokens with a given space delimiter (i.e., matching the string " "or regular expression /\s{1}/). When a token class represents more than one possible lexeme, the lexer often saves enough information to reproduce the original lexeme, so that it can be used in semantic analysis .
flex++ is a similar lexical scanner for C++ which is included as part of the flex package. The generated code does not depend on any runtime or external library except for a memory allocator (malloc or a user-supplied alternative) unless the input also depends on it.
A classic example of a problem which a regular grammar cannot handle is the question of whether a given string contains correctly nested parentheses. (This is typically handled by a Chomsky Type 2 grammar, also termed a context-free grammar .)
the subexpression can match the same input in multiple ways, or the subexpression can match an input string which is a prefix of a longer possible match; and after the repeated subexpression, there is an expression that matches something which the subexpression does not match. The second condition is best explained with two examples:
ZXing – Multiplatform open source barcode scanner / generator with versions available in Java (core project) and ports to ActionScript, C++, C#, ObjectiveC and Ruby. Python Bar Code 128 – This code appears to draw boxes one pixel wide.
java.nio (NIO stands for New Input/Output [1] [2]) is a collection of Java programming language APIs that offer features for intensive I/O operations. It was introduced with the J2SE 1.4 release of Java by Sun Microsystems to complement an existing standard I/O. NIO was developed under the Java Community Process as JSR 51. [3]