Source handling, lexical analysis and error reporting Syntax
16.1 Parameterless procedures
In this chapter we shall confine discussion to parameterless regular procedures or void functions in C ++ terminology, and discuss parameters and value-returning functions in the following chapter.16.1.1 Source handling, lexical analysis and error reporting
The extensions to be discussed in this chapter require no changes to the source handler, scanner or error reporter classes that were not pre-empted in the discussion in Chapter 14.16.1.2 Syntax
Regular procedure declaration is inspired by the way it is done in Modula-2, described in EBNF by Block = { ConstDeclarations | VarDeclarations | ProcDeclaration } CompoundStatement . ProcDeclaration = PROCEDURE ProcIdentifier ; Block ; . It might be thought that the same effect could be achieved with ProcDeclaration = PROCEDURE ProcIdentifier ; CompoundStatement ; . but the syntax first suggested allows for nested procedures, and for named constants and variables to be declared local to procedures, in a manner familiar to all Modula-2 and Pascal programmers. The declaration of a procedure is most easily understood as a process whereby a CompoundStatement is given a name. Quoting this name at later places in the program then implies execution of that CompoundStatement. By analogy with most modern languages we should like to extend our definition of Statement as follows: Statement = [ CompoundStatement | Assignment | ProcedureCall | IfStatement | WhileStatement | WriteStatement | ReadStatement ] . ProcedureCall = ProcIdentifier . However, this introduces a non-LL1 feature into the grammar, for now we have two alternatives for Statement namely Assignment and ProcedureCall that begin with lexically indistinguishable symbols. There are various ways of handling this problem: A purely syntactic solution for this simple language is possible if we re-factor the grammar as Statement = [ CompoundStatement | AssignmentOrCall | IfStatement | WhileStatement | WriteStatement | ReadStatement ] . AssignmentOrCall = Designator [ := Expression ] . so that a ProcedureCall can be distinguished from an Assignment by simply looking at the first symbol after the Designator. This is, of course, the approach that has to be followed when using CocoR. A simple solution would be to add the keyword CALL before a procedure identifier, as in Fortran, but this rather detracts from readability of the source program. Probably because the semantics of procedure calls and of assignments are so different, the solution usually adopted in a hand-crafted compiler is a static semantic one. To the list of allowed classes of identifier we add one that distinguishes procedure names uniquely. When the symbol starting a Statement is an identifier we can then determine from its symbol table attributes whether an Assignment or ProcedureCall is to be parsed assuming all identifiers to have been declared before use, as we have been doing.16.1.3 The scope and extent of identifiers
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» compilers and compiler generators 1996
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» Grammars and productions compilers and compiler generators 1996
» Classic BNF notation for productions
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» Phrase structure and lexical structure -productions
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» Type 1 Grammars Context-sensitive The Chomsky hierarchy
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» Terminal successors, the FOLLOW function, and LL1 conditions for non -free grammars
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» Alternative formulations of the LL1 conditions
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» Construction of simple recursive descent parsers
» Case studies compilers and compiler generators 1996
» Syntax error detection and recovery
» Construction of simple scanners
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» Automated construction of scanners and parsers
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» Synthesized and inherited attributes
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» Installation Input file preparation
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» Case study - a simple adding machine
» Character sets Comments and ignorable characters
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» Interfacing to support modules The parser interface
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» Case study - Understanding C declarations
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» 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
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» 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
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