Lecture 03: Languages Implementation Methods & Compilation

describe Compilation

[1] Translate high-level program (source language) into machine code (machine language) [3] Slow translation, fast execution [2] Use: Large commercial applications.

Describe Pure Interpretation

[1] Programs are interpreted by another program known as an interpreter. [2] Use: Small programs or when efficiency is not an issue.

Describe Hybrid Implementation Systems

[1] A compromise between compilers and pure interpreters. [2] Use: Small and medium systems when efficiency is not the first priority.

what are the phases of Compilation?

[1] lexical analysis [2] syntax analysis [3] Semantics analysis [4] code generation

what is lexical analysis

converts characters in the source program into lexical units

What is syntax analysis

transforms lexical units into parse trees which represent the syntactic structure of program

what is Semantics analysis

generate intermediate code

what is code generation

machine code is generated

What is a compiler

A compiler is a program that translates a program in a source language into an equivalent program in a target language.

What is the structure of a compiler?

(Source program->[Lexical analyser]->[Synax analyser]->[Semantic analyser]->[Code optomiser]->[Code generator]->Target program) everything in [] is also conected to a symbol table

what does the lexical Analysis entail?

[1] The lexical analyser (or scanner): reads the source program’s text (one character at a time); and returns a sequence of tokens to send to the next phase. [2] Tokens are symbolic names for the lexical elements of the source language

What is the Symbols Table

The symbol table is a data structure containing all the identifiers (together with their attributes) of a source program.

What are typical Attributes of variables?

type, size, scope.

What are typical attributes for methods procedures or functions

number of arguments and their types and passing mechanisms; the return type (if any).

What is Syntax Analisis (parsing)

[1] analyses the syntactic structure of the source program for valid syntax[2] input to a parser is the sequence of output tokens from the lexical analyser [3] It attempts to apply the rules that define the syntax of the language on the sequence of tokens

what is Semantic Analysis

determines if the source program (based on the AST and symbol table) is semantically valid.

What does AST stand for? and what is it?

Abstract syntax trees are data structures widely used in compilers to represent the structure of program code

What is Error Handling

[1] The three analysis phases of a compiler must be able to deal with errors in the source program. [2] On detecting an error a compiler should ideally: report the error in a helpful way, and continue processing to look for further errors.

What is Code Optimisation

[1] Attempts to improve the time and space requirements of a program, i.e., makes a smaller or faster or both. [2] Example optimisations include: -constant folding (e.g., replacing 3+7 with 10); -eliminating unreachable code

What is Code Generation

[1] The final task of the compiler is to generate code for a specific machine. In this phase we need to consider such [2] The output from this phase is usually programs in machine language or assembly language or code for a virtual machine.

What things may be considered during code generation

[1] Instruction selection: The machine language instr' to use [2] Instr' scheduling: The order to put those instr'[3] Register allocation: The allocation of variables to processor registers[4] Debug data generation if required so the code can be debugged

What is Pure Interpretation

An interpreter parse the source code and execute it directly, e.g., early versions of the Lisp and BASIC.

describe some dissadvantages of pure implimentation compared with compilation.

[1] Slower execution than compiled programs [2] Often requires more space

Why is pure interpritation slower than compilation?

[1] decoding high-level language statement is slower than decoding machine language instructions [2] Regardless how many times a statement is executed, it must be decoded every time.

Why does pure interpritation need more space than compilation?

the source code and the symbol table must be present during interpretation

give examples of Pure interpritation languages

Now rare for traditional high-level languages but has significant comeback with some Web scripting languages (e.g., JavaScript, PHP)

What is Hybrid Implementation Systems

A compromise between compilers and pure interpreters (not as fast as compiled languages, but faster than interpreted languages)

Describe the process used byHybrid Implementation Systems

A high-level language program is translated/compiled to an intermediate code that will be interpreted during execution.

with Hybrid Implementation Systems is the intermediate code ever translated further?

no never, Instead, a virtual machine is supplied that takes the intermediate language as its machine language, and interpret the intermediate code (much faster than it would be able to interpret a high-level language)

Give examples of some Hybrid Implementation Systems languages

E.g., Perl, Python, and MATLAB, JDK1.0

describe Just-in-Time Implementation Systems

[1] compile programs to an intermediate language[2] intermediate language is loaded into memory [3] segments/subprograms are translated into machine code just before its execution (or when they are called)[4] The machine code is kept for subsequent calls