Wirth’s EBNF notation
5.9.1 Wirth’s EBNF notation
In defining Pascal and Modula-2, Wirth came up with one of these many variations on BNF which has now become rather widely used Wirth, 1977. Further metasymbols are used, so as to express more succinctly the many situations that otherwise require combinations of the Kleene closure operators and the string. In addition, further simplifications are introduced to facilitate the automatic processing of productions by parser generators such as we shall discuss in a later section. In this notation for EBNF: Non-terminals are written as single words, as in VarDeclaration rather than the Var Declaration of our previous notation Terminals are all written in quotes, as in BEGIN rather than as themselves, as in BNF | is used, as before, to denote alternatives parentheses are used to denote grouping [ ] brackets are used to denote the optional appearance of a symbol or group of symbols { } braces are used to denote optional repetition of a symbol or group of symbols = is used in place of the ::= or symbol . is used to denote the end of each production are used in some extensions to allow comments can be handled by using the [ ] notation spaces are essentially insignificant. For example Integer = Sign UnsignedInteger . UnsignedInteger = digit { digit } . Sign = [ + | - ] . digit = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 . The effect is that non-terminals are less noisy than in the earlier forms of BNF, while terminals are noisier. Many grammars used to define programming language employ far more non-terminals than terminals, so this is often advantageous. Furthermore, since the terminals and non-terminals are textually easily distinguishable, it is usually adequate to give only the set of productions P when writing down a grammar, and not the complete quadruple { N, T, S, P }. As another example of the use of this notation we show how to describe a set of EBNF productions in EBNF itself: EBNF = { Production } . Production = nonterminal = Expression . . Expression = Term { | Term } . Term = Factor { Factor } . Factor = nonterminal | terminal | [ Expression ] | Expression | { Expression } . nonterminal = letter { letter } . terminal = ’ character { character } ’ | ’’ character { character } ’’ . character = implementation defined . Here we have chosen to spell nonterminal and terminal in lower case throughout to emphasize that they are lexical non-terminals of a slightly different status from the others like Production, Expression, Term and Factor. A variation on the use of braces allows the otherwise impossible specification of a limit on the number of times a symbol may be repeated - for example to express that an identifier in Fortran may have a maximum of six characters. This is done by writing the lower and upper limits as sub- and super-scripts to the right of the curly braces, as for example FortranIdentifier letter { letter | digit } 55.9.2 Semantic overtones
Parts
» compilers and compiler generators 1996
» Objectives compilers and compiler generators 1996
» Systems programs and translators
» The relationship between high-level languages and translators
» T-diagrams Classes of translator
» Phases in translation compilers and compiler generators 1996
» Multi-stage translators compilers and compiler generators 1996
» Interpreters, interpretive compilers, and emulators
» Using a high-level host language Porting a high level translator
» Bootstrapping Self-compiling compilers compilers and compiler generators 1996
» The half bootstrap compilers and compiler generators 1996
» Bootstrapping from a portable interpretive compiler A P-code assembler
» Simple machine architecture compilers and compiler generators 1996
» Addressing modes compilers and compiler generators 1996
» Machine architecture Case study 1 - A single-accumulator machine
» Instruction set Case study 1 - A single-accumulator machine
» A specimen program Case study 1 - A single-accumulator machine
» An emulator for the single-accumulator machine
» A minimal assembler for the machine
» Machine architecture Case study 2 - a stack-oriented computer
» Instruction set Case study 2 - a stack-oriented computer
» Specimen programs Case study 2 - a stack-oriented computer
» An emulator for the stack machine
» Syntax, semantics, and pragmatics
» Languages, symbols, alphabets and strings Regular expressions
» Grammars and productions compilers and compiler generators 1996
» Classic BNF notation for productions
» Simple examples compilers and compiler generators 1996
» Phrase structure and lexical structure -productions
» Semantic overtones The British Standard for EBNF Lexical and phrase structure emphasis
» One- and two-pass assemblers, and symbol tables
» Source handling Towards the construction of an assembler
» Lexical analysis Towards the construction of an assembler
» Syntax analysis Towards the construction of an assembler
» Symbol table structures The first pass - static semantic analysis
» The second pass - code generation
» Symbol table structures The first pass - analysis and code generation
» Error detection compilers and compiler generators 1996
» Simple expressions as addresses
» Improved symbol table handling - hash tables
» Macro processing facilities compilers and compiler generators 1996
» Conditional assembly compilers and compiler generators 1996
» Relocatable code compilers and compiler generators 1996
» Further projects compilers and compiler generators 1996
» Equivalent grammars Case study - equivalent grammars for describing expressions
» Useless productions and reduced grammars -free grammars
» Ambiguous grammars compilers and compiler generators 1996
» Type 1 Grammars Context-sensitive The Chomsky hierarchy
» The relationship between grammar type and language type
» EBNF description of Clang A sample program
» Context sensitivity Deterministic top-down parsing
» Terminal successors, the FOLLOW function, and LL1 conditions for non -free grammars
» Further observations Restrictions on grammars so as to allow LL1 parsing
» Alternative formulations of the LL1 conditions
» The effect of the LL1 conditions on language design
» Construction of simple recursive descent parsers
» Case studies compilers and compiler generators 1996
» Syntax error detection and recovery
» Construction of simple scanners
» LR parsing compilers and compiler generators 1996
» Automated construction of scanners and parsers
» Embedding semantic actions into syntax rules
» Attribute grammars compilers and compiler generators 1996
» Synthesized and inherited attributes
» Classes of attribute grammars
» Case study - a small student database
» Installation Input file preparation
» Execution Output from CocoR Assembling the generated system
» Case study - a simple adding machine
» Character sets Comments and ignorable characters
» Pragmas User names The scanner interface
» Syntax error recovery Parser specification
» Grammar checks Semantic errors
» Interfacing to support modules The parser interface
» Essentials of the driver program Customizing the driver frame file
» Case study - Understanding C declarations
» Case study - Generating one-address code from expressions
» Case study - Generating one-address code from an AST
» Case study - How do parser generators work?
» Project suggestions compilers and compiler generators 1996
» Overall compiler structure compilers and compiler generators 1996
» A hand-crafted source handler
» A hand-crafted scanner Lexical analysis
» A CocoR generated scanner Efficient keyword recognition
» A hand-crafted parser A CocoR generated parser
» Syntax error handling in hand-crafted parsers
» Error reporting The symbol table handler
» Other aspects of symbol table management - further types
» The code generation interface
» Code generation for a simple stack machine
» Machine tyranny Other aspects of code generation
» Abstract syntax trees as intermediate representations
» Simple optimizations - constant folding
» Simple optimizations - removal of redundant code
» Generation of assembler code
» Source handling, lexical analysis and error reporting Syntax
» The scope and extent of identifiers
» Symbol table support for the scope rules
» Parsing declarations and procedure calls
» Hypothetical machine support for the static link model
» Code generation for the static link model
» Hypothetical machine support for the display model
» Code generation for the display model
» Relative merits of the static link and display models
» Syntax and semantics compilers and compiler generators 1996
» Symbol table support for context-sensitive features
» Actual parameters and stack frames
» Hypothetical stack machine support for parameter passing
» Semantic analysis and code generation in a hand-crafted compiler
» Semantic analysis and code generation in a CocoR generated compiler
» Scope rules Language design issues
» Function return mechanisms Language design issues
» Context sensitivity and LL1 conflict resolution Fundamental concepts
» Parallel processes, exclusion and synchronization
Show more