COMP313A Programming Languages

1. COMP313A Programming Languages Overview of the Compilation Process

2. skeletal source program preprocessor source program compiler target assembly program assembler relocatable machine code loader/link-editor absolute machine code

3. source program lexicalanalyser syntaxanalyser symbol table manager semanticanalyser error handler code optimiser code generator target program

4. Type 0 Unrestricted Grammar Type 1 Context-Sensitive Grammar Type 2 Context Free Grammar Type 3 Regular Grammar Chomsky’s Grammar Hierarchy

5. Grammars • Type 3 (regular) • A  wB, A  w (right linear) • w is a string of Terminals • A and B are Non-Terminals • Finite state automata • Type 2 (context free) • A   • A is a Non-terminal •  is a member of T  N   (can be empty) • Equivalent to a push-down automaton

6. Grammars • Type 1 (context sensitive) •  A    B  • A becomes B in the context of  …  • Complex for computer analysis • Type 0 (unrestricted) •   , •  and  are unrestricted sequences,  is not null • languages formed from Type 0 grammars can be recognised by non-deterministic Turing machines

7. Lexical Analysis object_position = calculate_position( robot_coordinates, robot_heading, range, error) Need to find the words i.e. tokens

8. Lexical Analysis • Uses a regular grammar for specifying the rules for forming “words” / tokens

9. Syntax Analysis • Hierarchical Analysis • Groups tokens into grammatical phrases • Parse Tree • Use syntax rules (context free grammars/BNF) to perform the analysis

10. Expression ::= id Expression ::= num Expression ::= Expression + Expression Expression ::= Expression * Expression

11. assignment statement = expression identifier position expression + expression identifier * expression expression initial identifier identifier rate 60

12. = + position initial * rate 60

13. Semantic Analysis • Checks source program for semantic errors • Type checking • Gathers type information for code generation

14. = + position initial * rate inttoreal 60

15. Symbol Table Management • Records identifiers used in source program • Collects information about various attributes of each identifier • Storage allocation • Type • Scope • Procedure names – ?????

16. Error Detection and Reporting • Lexical errors • Syntax errors • Semantic errors

17. Code Optimisation • Improve code so it runs faster • Where does program spend most of its time?

18. Code generation • Generation of target code • Relocatable machine code or assembler code • Memory locations are selected for each of the variables • Assignment of variables to registers

19. MOVF id3, R2 MULF #60.0, R2 MOVF id2, R1 ADDF R2, R1 MOVF R1, id1

20. Analysis versus Synthesis • Back end versus front end of the compiler