Sommerville-Software-Engineering-10ed

190 Chapter 6 ■ Architectural design
Lexical
analyzer
Syntax
analyzer
Semantic
analyzer
Formatter
Abstract
syntax tree
Grammar
definition
Optimizer
Figure 6.21 A
repository architecture
for a language
processing system
Editor
Symbol
table
Repository
Output
definition
Code
generator
program to be executed, and a translator converts these into instructions for an abstract
machine. These instructions are then interpreted by another component that fetches
the instructions for execution and executes them using (if necessary) data from the
environment. The output of the process is the result of interpreting the instructions on
the input data.
For many compilers, the interpreter is the system hardware that processes machine
instructions, and the abstract machine is a real processor. However, for dynamically
typed languages, such as Ruby or Python, the interpreter is a software component.
Programming language compilers that are part of a more general programming
environment have a generic architecture (Figure 6.21) that includes the following
components:
1. A lexical analyzer, which takes input language tokens and converts them into an
internal form.
2. A symbol table, which holds information about the names of entities (variables,
class names, object names, etc.) used in the text that is being translated.
3. A syntax analyzer, which checks the syntax of the language being translated. It
uses a defined grammar of the language and builds a syntax tree.
4. A syntax tree, which is an internal structure representing the program being
compiled.
5. A semantic analyzer, which uses information from the syntax tree and the symbol
table to check the semantic correctness of the input language text.
6. A code generator, which “walks” the syntax tree and generates abstract
machine code.
Other components might also be included that analyze and transform the syntax
tree to improve efficiency and remove redundancy from the generated machine code.