Programming Language Concepts Chapter 4

addChar

Adds the character in nextChar to the end of lexeme.

Responsibilities of a syntax analyzer, or parser

Determine whether the input program is syntactically correct.Produce a parse tree.

State Diagram

Directed Graph (it recognizes names, integer literals, parentheses, and arithmetic operators)

Parsers are categorized by

Top Down Bottom up

A recursive-descent parser

is coded directly from the BNF description of the syntax of a language.An alternative is to use a parsing table rather than code.

Bottom-up parsers are often called

shift-reduce algorithms

Three ways to Implement Programming Languages

Compilation, Pure interpretation, and Hybrid implementation

lookup

Computes the token code for single-character tokens (parentheses and arithmetic operators).

Syntax Analyzer

Deals with large-scale constructs, such as expressions, statements, and program units.

Lexical Analyzer

Deals with small-scale language constructs, such as names and numeric literals.

getChar

Gets the next input character and puts it in a global variable namednextChar. Also determines the character class of the input character andputs it in the global variable charClass.

Efficiency

It becomes easier to optimize the lexical analyzer.

Which analyzer does the 3 use

Lexical and Syntax Analyzer

Mixed strings (terminals and/or nonterminals)

Lowercase Greek letters (α, β,γ, δ)

Terminal symbols

Lowercase letters at the beginning of the alphabet (a, b, ...)

Strings of terminals

Lowercase letters at the end of the alphabet (w, x, y, z)

Parsing

Often reffered to as Syntax Analysis

Bottom-up

Parsers build the tree from the leaves upward to the root.

Top-down

Parsers build the tree from the root downward to the leaves.

Simplicity

Removes the details of lexical analysis from the syntax analyzer which makes it smaller and less complex

Why do the compilers separate the analyzers?

Simplicity, Efficiency, and Portability

getNonBlank

Skips white space

Handle

The correct RHS to reduce

LL Parser

The first L in LL speci-fies a left-to-right scan of the input; the second L specifies that a leftmost deriva-tion is generated

Portability

The lexical analyzer reads source files, so it may be platform-dependent

State Diagram have:

The nodes are labeled with state names. The arcs are labeled with input characters. An arc may also include actions to be done when the transition is taken

Advantages of LR parsers

They can be built for all programming languages. They can detect syntax errors as soon as possible in a left-to-right scan. The LR class of grammars is a proper superset of the class parsable by LL pars-ers

Nonterminal symbols

Uppercase letters at the beginning of the alphabet (A, B

Terminals or nonterminals

Uppercase letters at the end of the alphabet (W, X,Y, Z)

simple phrase

a phrase that is derived from a non-terminal in a single step.

phrase

a string consisting of all of the leaves of the partial parse tree that is rooted at one particular internal node of the whole parse tree.

Lexemes

are recognized by matching the input against patterns.

Tokens

are usually coded as integer values, but for the sake of readability, theyare often referenced through named constants

A lexical analyzer collects

collects input characters into groups (lexemes) and assigns an internal code (a token) to each group

LR

he Lspecifies a left-to-right scan and the R specifies that a rightmost derivation is generated

pairwise disjointness test

used to test a non-left-recursive grammar todetermine whether it can be parsed in a top-down fashion. This test requirescomputing FIRST sets