interpreter + stages of compilation

Order of compilation stages

• Lexical

• Syntax

• Code generation

• Code optimisation

Tasks of syntax compilation stage

• Constructing a parse tree

• Checking that rules of grammar/language has been obeyed

• Production of an error report

Reasons for optimisation of code

• Minimises amount of memory used

• Minimises execution time

Explain how an interpreter executes a program without producing a complete translate version of it

• Examines source code one statement at a time

• Checks each statement for errors

  • If no error is found the statement is executed

  • If an error is found this is reported and the interpreter halts

• Interpretation is repeated for every iteration in repeated sections of code

• Interpretation has to be repeated every time the program is run

Lexical analysis description

• Converting a sequence of characters into a sequence of tokens

Syntax analysis description

• Using parsing algorithms to interpret the meaning of a sequence of tokens

Code generation description

• Converting an intermediate representation of source code into an executable form

Optimisation description

• Minimising a program’s execution time and memory requirement

Purpose of syntax analysis

• Checks that the code matches the grammar of the language

• Syntax errors are reported

• A parse tree is produced

Process of executing a program using an interpreter

• The interpreter translates the source code one line at a time

• If the line is syntax error free, it is executed

• It is not stored in an executable format

• If an error is found, the program halts with an error message

• Each line must be translated every time it is run (including lines running multiple times, like loops)

Lexical analysis during program compilation

• First stage of compilation

• White space and comments are removed

• Takes modified source code and converts it into a series of tokens

• Each token is categorised and assigned  type

• Identifiers are stored in a table

• If it finds invalid tokens, it generates an error

• Acceptable data then passes to the syntax analyser

Syntax analysis during program compilation

• Second stage of compilation

• Takes input from the lexical analyser in the form of token streams

• Uses parsing algorithms to interpret the meaning of a sequence of tokens

• Source code is analysed / Checking that the rules of the grammar have been obeyed

• Output from phase is a parse tree

• Syntax errors are reported here

Purpose of lexical analysis during compilation of a program

• Convert high-level source code

  • That can be sent to the parser for syntax analysis

• To create a symbol(token) table

• To remove unnecessary white space and comments from the code

Purpose of optimisation stage in compilation of a program

• Minimising program storage

• Minimising CPU time

• Minimising memory use

• Minimising program execution time

Process of optimisation during compilation of a program

• To identify and remove redundant code // to simplify expressions // To reorder the code

  • So that storage size, memory use, power consumption, program execution time and CPU time is minimised