1. Chapter3: Language Translation issues
Programming language Syntax
Key criteria concerning syntax
Basic syntactic concepts
Overall Program-Subprogram structure
Stages in Translation
Analysis of the source program
Synthesis of the object program
Bootstrapping

2. What is Syntax
The syntax of a programming language describes the structure of programs without any consideration of their meaning.

3. Key criteria concerning syntax
Readability – a program is considered readable if the algorithm and data are apparent by inspection.
Writeability – ease of writing the program.
Verifiability – ability to prove program correctness (very difficult issue)
Translatability – ease of translating the program into executable form.
Lack of ambiguity – the syntax should provide for ease of avoiding ambiguous structures

4. Basic syntactic concepts
Character set – The alphabet of the language. Several different character sets are used: ASCII, EBCIDIC, Unicode
Identifiers – strings of letters of digits usually beginning with a letter
Operator Symbols – +-*/
Keywords or Reserved Words – used as a fixed part of the syntax of a statement

5. Basic syntactic concepts
Noise words – optional words inserted into statements to improve readability
Comments – used to improve readability and for documentation purposes. Comments are usually enclosed by special markers
Blanks – rules vary from language to language. Usually only significant in literal strings

6. Basic syntactic concepts
Delimiters – used to denote the beginning and the end of syntactic constructs
Expressions – functions that access data objects in a program and return a value
Statements – these are the sentences of the language, they describe a task to be performed

7. Overall Program-Subprogram Structure
Separate subprogram definitions: Separate compilation, linked at load time E.G. C/C++
Separate data definitions: General approach in OOP.
Nested subprogram definitions: Subprogram definitions appear as declarations within the main program or other subprograms. E.G. Pascal

8. Overall Program-Subprogram Structure
Separate interface definitions:
C/C++ header files
Data descriptions separated from executable statements. A centralized data division contains all data declarations. E.G. COBOL
Unseparated subprogram definitions: No syntactic distinction between main program statements and subprogram statements.
E.G BASIC

9. Stages in Translation Analysis of the source program
Synthesis of the object program
Bootstrapping

10. Analysis of the source program
Lexical analysis (scanning) – identifying the tokens of the programming language: keywords, identifiers, constants and other symbols
In the program
void main()
{ printf("Hello World\n"); }
the tokens are
void, main, (, ), {, printf, (, "Hello World\n", ), ;, }

11. Syntactic and semantic analysis
Syntactic analysis (parsing) – determining the structure of the program, as defined by the language grammar.
Semantic analysis - assigning meaning to the syntactic structures
Example: int variable1;
meaning: 4 bytes for variable1 , a specific set of operations to be used with variable1.

12. Basic semantic tasks
The semantic analysis builds the bridge between analysis and synthesis.
Basic semantic tasks:
Symbol–table maintenance
Insertion of implicit information
Error detection
Macro processing
Result : an internal representation, suitable to be used for code optimization and code generation.

13. Synthesis of the object program
Three main steps:
Optimization - Removing redundant statements
Code generation - generating assembler commands with relative memory addresses for the separate program modules - obtaining the object code of the program.
Linking and loading - resolving the addresses - obtaining the executable code of the program.

14. Optimization example Statements in yellow can be removed
Assembler code not optimized:
LOAD_R B
ADD_R C
STORE_R Temp1
LOAD_R Temp1
ADD_R D
STORE_R Temp2
LOAD_R Temp2
STORE_R A
Intermediate code:
Temp1 = B + C
Temp2 = Temp1 + D
A = Temp2
Statements in yellow can be removed

15. Bootstrapping
The compiler for a given language can be written in the same language.
a program that translates some internal representation into assembler code
the programmer manually re-writes the compiler into the internal representation, using the algorithm that is encoded into the compiler.
From there on the internal representation is translated into assembler and then into machine language.