Bottom-up emphasizes coding and early testing, which can begin as soon as the first module has been specified.

* Bottom-up approach: Once we formulate the solution to a problem recursively as in terms of its subproblems, we can try reformulating the problem in a bottom-up fashion: try solving the subproblems first and use their solutions to build-on and arrive at solutions to bigger subproblems.

Bottom-up input arrives at layer 4 ( L4 ), whence it propagates to L2 and L3 for recognition of the invariant content.

* Online lecture on Molecular Electronics and the Bottom-up View of Electronic Conduction by S. Datta

Bottom-up processing is a type of information processing based on incoming data from the environment to form a perception.

Bottom-up parsing is a strategy for analyzing unknown data relationships that attempts to identify the most fundamental units first, and then to infer higher-order structures from them.

See Top-down parsing and Bottom-up parsing.

Bottom-up approaches seek to have smaller ( usually molecular ) components built up into more complex assemblies, while top-down approaches seek to create nanoscale devices by using larger, externally controlled ones to direct their assembly.

Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to ( a ) self-organize or self-assemble into some useful conformation, or ( b ) rely on positional assembly.

" Bottom-up " ( or " small chunk ") cognition is akin to focusing on the detail primarily, rather than the landscape.

* Integrated Parallel Bottom-up and Top-down Approach.

Bottom-up parsing identifies and processes the text's lowest-level small details first, before its mid-level structures, and leaving the highest-level overall structure to last.

Bottom-up parsing lazily waits until it has scanned and parsed all parts of some construct before committing to what the combined construct is.

* Bottom-up models are often the result of a reengineering effort.

Bottom-up approaches, in contrast, use the chemical properties of single molecules to cause single-molecule components to ( a ) self-organize or self-assemble into some useful conformation, or ( b ) rely on positional assembly.

Bottom-up processes are generally driven by the abiotic conditions required for primary producers to grow, such as availability of light and nutrients, and the subsequent transfer of energy to consumers at higher trophic levels.

Bottom-up effects occur when the population density of a resource affects the population of the resources ’ consumer.

Objective Elaboration: Bottom-up thinking in which facts are scrutinized without bias ; seeking truth wherever it might lead.

The recognizer can be easily modified to create a parse tree as it recognizes, and in that way can be turned into a parser.

The LR parser can recognize any deterministic context-free language in linear-bounded time.

This reduces the power of the parser because, as the following example depicts, dropping the lookahead info can confuse the parser as to which grammar rule to pick next, resulting in a reduce / reduce conflict.

For the same reason error reporting can be quite hard because LALR parser errors cannot always be interpreted into messages meaningful for the end user.

* JS / CC JavaScript based implementation of a LALR ( 1 ) parser generator, which can be run in a web-browser or from the command-line.

When using an LR parser within some larger program, you can usually ignore all the mathematical details about states, tables, and generators.

All of the parsing actions and outputs and their timing can be simply understood by viewing the LR parser as just a shift-reduce parser with some nifty decision method.

For example, when a string is coerced, the parser turns as much of the string ( starting from the left ) into a number as it can, then discards the rest.

Because its input can be described with a formal grammar, it can be used in parser design.

A regular expression is written in a formal language that can be interpreted by a regular expression processor, which is a program that either serves as a parser generator or examines text and identifies parts that match the provided specification.

Not every SGML parser can necessarily process every SGML document.

If such a parser exists for a certain grammar and it can parse sentences of this grammar without backtracking then it is called an LL ( k ) grammar.

An LL parser is called an LL (*) parser if it is not restricted to a finite k tokens of lookahead, but can make parsing decisions by recognizing whether the following tokens belong to a regular language ( for example by use of a Deterministic Finite Automaton ).

Parrot provides a suite of compiler-writing tools which includes the Parser Grammar Engine ( PGE ), a hybrid parser-generator that can express a recursive descent parser as well as a operator-precedence parser, allowing free transition between the two in a single grammar.

Some implementations do not neatly fit either category: a DOM approach can keep its persistent data on disk, cleverly organized for speed ( editors such as SoftQuad Author / Editor and large-document browser / indexers such as DynaText do this ); while a SAX approach can cleverly cache information for later use ( any validating SAX parser keeps more information than described above ).

Compiler-compilers exist in many flavors, including bottom-up rewrite machine generators ( see JBurg ) used to tile syntax trees according to a rewrite grammar for code generation, and attribute grammar parser generators ( e. g. ANTLR can be used for simultaneous type checking, constant propagation, and more during the parsing stage ).

A grammar that can be parsed by an SLR parser but not by an LR ( 0 ) parser is the following:

The task of the parser is essentially to determine if and how the input can be derived from the start symbol of the grammar.

Command line programs often start with an option parser that translates command line switches into flags in the sense of this article.

An Earley parser is an example of such an algorithm, while the widely used LR and LL parsers are simpler algorithms that deal only with more restrictive subsets of context-free grammars.

The parser is seeded with S ( 0 ) consisting of only the top-level rule.

The simplification that takes place results in a parser with significantly reduced memory requirements but decreased language recognition power.

Usually this happens with the addition of some hand-written code that extends the power of the parser.

To address this shortcoming, in 1969, Frank DeRemer proposed two simplified versions of the LR parser, namely the Look-Ahead LR ( LALR ) and the Simple LR parser that had much lower memory requirements at the cost of less language recognition power with the LALR parser being the most powerful alternative.

As with other types of LR parser, an LALR parser is quite efficient at finding the single correct bottom-up parse in a single left-to-right scan over the input stream, because it doesn't need to use backtracking.

Being a lookahead parser by definition, it always uses a lookahead, with LALR ( 1 ) being the most common case.

as is the case with any parser based on the LR ( 1 ) parser.

As with other shift-reduce parsers, an LR parser works by doing some combination of Shift steps and Reduce steps.

If the input has no syntax errors, the parser continues with these steps until all of the input has been consumed and all of the parse trees have been reduced to a single tree representing an entire legal input.

To avoid guessing, the LR parser often looks ahead ( rightwards ) at the next scanned symbol, before deciding what to do with previously scanned symbols.

An extrinsic evaluation would run the parser with some other POS tagger, and then with the new POS tagger, and compare the parsing accuracy.

* Lex ( and Flex lexical analyser ), the token parser commonly used in conjunction with Yacc ( and Bison ).

Zork distinguished itself in its genre as an especially rich game, in terms of both the quality of the storytelling and the sophistication of its text parser, which was not limited to simple verb-noun commands (" hit troll "), but recognized some prepositions and conjunctions (" hit the troll with the Elvish sword ").

Given a grammar in GNF and a derivable string in the grammar with length n, any top-down parser will halt at depth n.

It parses the input from Left to right, and constructs a Leftmost derivation of the sentence ( hence LL, compared with LR parser ).

Languages based on grammars with a high value of k have traditionally been considered to be difficult to parse, although this is less true now given the availability and widespread use of parser generators supporting LL ( k ) grammars for arbitrary k.