Programming language translators

• Understand the role of an assembler, compiler and interpreter
• Compilation


  1. Lexical analysis

  2. Syntax analysis

  3. Code generation

  4. Optimization
• Assembler


  Translates assembly code into machine code
• Assembly code


  Low-level language, with each instruction almost equivalent to one machine code instruction
• Compiler


  Translates high-level language into machine code
• Different hardware platforms


  Require different compilers
• Compiler process


  1. Source code input

  2. Compile

  3. Object code (executable machine code) output
• Object code can be saved and run without the presence of the compiler
• Interpreter


  Translates high-level language into machine code
• Intermediate language such as bytecode is produced as the final output by some compilers and is subsequently used
• Linkers and loaders


  Their function is described
• Libraries


  Their use is described
• Interpreter


  A type of programming language translator that analyzes the source code, checks for syntax errors, and executes the code line by line
• Interpreter operation


  1. Programmer writes program

  2. Interpreter analyzes program for syntax errors

  3. Interpreter translates program to machine code

  4. Interpreter executes program
• Python program with syntax error

  • print ("abc)

  SeTAT1

  6 print ("a-be)

  7 print ("goodbye")
• When the program runs, it produces a NameError because the variable 'n' is not defined
• Python program with syntax error (missing closing bracket)

  • 3 chatb

  4 print("s+b", c)

  5e-a-b

  6 print ("a-b

  7 print ("goodbye")
• When the program runs, it does not execute any of the code but produces a SyntaxError because of the missing closing bracket
• The interpreter scans through the whole program checking for certain types of errors before executing any of it
• Bytecode


  Many languages are not only compiled or only interpreted, there are various possibilities in between such as bytecode
• Bytecode


  1. Compiling the source code into bytecode

  2. Interpreting the resulting bytecode
• Bytecode


  • The bytecode may be compiled once and for all, with errors detected before execution as in Python
  • A change in the source code requires recompiling the bytecode
• Bytecode


  • Achieves platform independence by abstracting away differences between computer architectures and operating systems
  • Provides an extra security layer by allowing the bytecode interpreter to execute the code rather than the program itself
• Compiling Python to Java bytecode

  1. Using the Jython compiler

  2. Executing the Java bytecode with the Java interpreter
• Compilers


  • The object code can be saved and run without needing to recompile
  • The object code executes faster than interpreted code
  • The object code is more secure as it cannot be easily read
• Interpreters


  • Provide platform independence by running the source code on any machine with the appropriate interpreter
  • Useful for program development as there is no need for lengthy recompilation
• Stages of compilation


  1. Lexical analysis

  2. Syntes analysis

  3. Code generation and optimisation
• Lexical analysis performs the following functions:
• Lexical analysis


  1. Removes superfluous spaces

  2. Converts all comments to spaces

  3. Performs simple error checking
• The lexical analyser will not detect misspelt keywords or undeclared variables, this is the job of the syntax analyser
• Tokens


  Unique symbols that replace keywords, constants and identifiers in the source code
• Symbol table


  Contains an entry for every keyword (reserved word) and identifier in the program, including information about the item such as its kind, type, run-time address/value, and pointers to accessing information
• Typical entries in a symbol table


  • input (keyword)
  • pi (constant, real, 3.14159)
  • radius (variable, real, (7))
  • operator
  • a20a (variable, real, (?))
  • numSides (array, integer, (?))
• The lexical analyser puts the anther and to run-in the symbol table so th can replace them in the source code by tokens
• The lexical analyser will not fill in the end of item and Type of le done later by the syntax analyser
• The symbol table must be organised in such a way that entries can be found as quickly as posable
• Hash table


  A common way of organising the symbol table where the keyword or identifier is hashed to produce an any sub
• Synonyms (colision) are inevitable in a hash table, and a common way of handing the is to store the synonym in the neat avalable too space in the table
• Syntax analysis


  The process of chamining whether the sequence of input characters, symbols, or tokens form a valid sentence in the language
• Parsing


  The task of systematically applying the set of rules to aach statement to determine whether it is valid