COMS W4115
Programming Languages and Translators
Lecture 4: Language Processing Tools
February 4, 2008

Lecture Outline

1. Review
2. Language design issues
3. Language processing tools
4. Structure of a compiler
5. Reading

1. Review

• Project teams should now be formed
• Language whitepaper: due February 27, 2008
• Concurrency

2. Language Design Issues

• Syntax: specifies the structure of a well-formed program
• Semantics: specifies the meaning of a program
• Computational model
• von Neumann
• functional
• logic or constraint-based
• dataflow
• object oriented
• scripting
• Programming style
• imperative ("how")
• declarative ("what")
• Names
• A name is a character string used to represent a program element.
• In C, each name has a storage class that specifies where it is and a type that specifies what it is
• Bindings
• A binding is an association between a name and the object it represents.
• Binding time
• Time at which a binding is created.
• Binding times range from language design time to run time.
• Bindings done at run time are dynamic; otherwise, they are static.
• Scope
• The textual region of a program in which a binding is active.
• C is statically scoped; the binding between names and objects can be determined at compile time.
• Control flow
• Specifies order in which operations are executed
• Principal mechanisms
• sequencing; e.g., begin . . . end
• selection: e.g., if-then
• iteration: e.g., while-loops
• procedures/recursion
• concurrency
• nondeterminism
• Structured vs. unstructured control flow
• See E.W. Dijkstra, Go To statement considered harmful, Comm. ACM, 11(3), pp. 147-148, March 1968.
• Types
• types determine the permissible values and operations within a program
• they provide an implicit context for operations
• they help eliminate bugs in programs at compile time
• a type system is a set of rules for
1. defining and associating types with various parts of a program
2. defining type equivalence, compatability, and inference
• In C the fundamental types are
• char
• integer
• floating point
• enumeration
• void
• In C the derived types are
• arrays of objects of a given type
• functions returning objects of a given type
• pointers to objects of a given type
• structures containing a sequence of objects of various types
• unions containing any one of several objects of various types
• Data abstraction and object orientation

3. Language Processing Tools

• Basic compiler
• Interpreter
• Bytecode interpreter
• Just-in-time compiler
• Linker and loader
• Preprocessor
• Compiler-compiler
• Compiler component generators
• lex, flex
• yacc, bison
• antlr
• Debugger
• Profiler
• Make facility
• Version control
• Integrated software development environment
• See GCC, the GNU Compiler Collection for compilers from GNU

4. Structure of a Compiler

• Front end: analysis
• Back end: synthesis
• IR: Intermediate representation(s)
• Phases
• lexical analyzer (scanner)
• syntax analyzer (parser)
• semantic analyzer
• intermediate code generator
• machine-independent code optimizer
• code generator
• machine-dependent code optimizer
• Symbol table
• Error handler
• See Fig. 1.6, ALSU p. 5.

5. Reading

• ALSU Chapters 1 and 2.