UNIT-02 LANGUAGE PROCESSORS

INTRODUCTION

Language Processors (Assembler, Compiler and Interpreter)

Language Processors –

Assembly language is machine dependent yet mnemonics that are being used to represent instructions in it are not directly understandable by machine and high Level language is machine independent. A computer understands instructions in machine code, i.e. in the form of 0s and 1s. It is a tedious task to write a computer program directly in machine code. The programs are written mostly in high level languages like Java, C++, Python etc. and are called source code. These source code cannot be executed directly by the computer and must be converted into machine language to be executed. Hence, a special translator system software is used to translate the program written in high-level language into machine code is called Language Processor and the program after translated into machine code (object program / object code).

The language processors can be any of the following three types:

1. Compiler –
   The language processor that reads the complete source program written in high level language as a whole in one go and translates it into an equivalent program in machine language is called as a Compiler.
   Example: C, C++, C#, Java 

        In a compiler, the source code is translated to object code successfully if it is free of errors. The         compiler specifies the errors at the end of compilation with line numbers when there are any               errors in the source code. The errors must be removed before the compiler can successfully                 recompile the source code again.

   2. Assembler –

      The Assembler is used to translate the program written in Assembly language into                machine code. The source program is a input of assembler that contains assembly                language instructions. The output generated by assembler is the object code or                    machine code understandable by the computer.
    

   3.Interpreter –

   The translation of single statement of source program into machine code is done by             language processor and executes it immediately before moving on to the next line is            called an interpreter. If there is an error in the statement, the interpreter terminates its           translating process at that statement and displays an error message. The interpreter moves on to the next line for execution only after removal of the error. An Interpreter directly executes instructions written in a programming or scripting language without previously converting them to an object code or machine code.

Example: Perl, Python and Matlab.

Difference between Compiler and Interpreter –

COMPILER	INTERPRETER
A compiler is a program which coverts the entire source code of a programming language into executable machine code for a CPU.	interpreter takes a source program and runs it line by line, translating each line as it comes to it.
Compiler takes large amount of time to analyze the entire source code but the overall execution time of the program is comparatively faster.	Interpreter takes less amount of time to analyze the source code but the overall execution time of the program is slower.
Compiler generates the error message only after scanning the whole program, so debugging is comparatively hard as the error can be present any where in the program.	Its Debugging is easier as it continues translating the program until the error is met
Generates intermediate object code.	No intermediate object code is generated.
Examples: C, C++, Java	Examples: Python, Perl
Difference between Compiler and Assembler: COMPILER ASSEMBLER Compiler converts the source code written by the programmer to a machine level language. Assembler converts the assembly code into the machine code. Compiler input source code. Assembler input assembly language code. It converts the whole code into machine language at a time. But the Assembler can’t do this at once. A Compiler is more intelligent than an Assembler. But, an Assembler is less intelligent than a Compiler. The compilation phases are lexical analyzer, syntax analyzer, semantic analyzer, intermediate code generated, a code optimizer, code generator, and error handler Assembler makes two phases over the given input, first phase and the second phase. The output of compiler is a mnemonic version of machine code. The output of assembler is binary code. C, C++, Java, and C# are examples of compiled languages. GAS, GNU is an example of an assembler.

EXPLAIN LANGUAGE PROCESSING ACTIVITIES:-

Language Processing Activities Language Processing activities arise due to the differences between the manner in which a software designer describes the ideas concerning the behaviour of a software and the manner in which these ideas are implemented in a computer system. the interpreter is a language translator. This leads to many similarities between are Translators and interpreters. From a practical viewpoint many differences also exist between translators and interpreters. The absence of a target program implies the absence of an output interface the interpreter. Thus the language processing activities of an interpreter cannot be separated from its program execution activities. Hence we say that an interpreter 'executes' a program written in a PL.
    The fundamental language processing activities can be divided into those that bridge the specification gap and those that bridge the execution gap. We name these activities as
1. Program generation activities 
2. Program execution activities. 

A program generation activity aims at automatic generation of a program. The source languages specification language of an application domain and the target language is typically a procedure oriented PL. A Program execution activity organizes the execution of a program written in a PL on computer system. Its source language could be a procedure-oriented language or a problem oriented language.

FUNDAMENTALS OF LANGUAGE PROCESSING :-

 Language Processing = Analysis of SP + Synthesis of TP.  

We refer to the collection of language processor components engaged in analyzing a source program as the analysis phase of the language processor. Components engaged in synthesizing a target program constitute the synthesis phase. A specification of the source language forms the basis of source program analysis. The specification consists of three components: 

1. Lexical rules:- which govern the formation of valid lexical units in the source language.

2. Syntax rules:- which govern the formation of valid statements in the source language.

3. Semantic rules:- which associate meaning with valid statements of the language. 

FUNDAMENTAL OF LANGUAGE SPECIFICATION

 A specification language is a formal language in computer science used during systems analysis, requirements analysis, and systems design to describe a system at a much higher level than a programming language, which is used to produce the executable code for a system.

Specification languages are generally not directly executed. They are meant to describe the what, not the how. Indeed, it is considered as an error if a requirement specification is cluttered with unnecessary implementation detail.

A common fundamental assumption of many specification approaches is that programs are modelled as algebraic or model-theoretic structures that include a collection of sets of data values together with functions over those sets. This level of abstraction coincides with the view that the correctness of the input/output behaviour of a program takes precedence over all its other properties.

In the property-oriented approach to specification (taken e.g. by CASL), specifications of programs consist mainly of logical axioms, usually in a logical system in which equality has a prominent role, describing the properties that the functions are required to satisfy — often just by their interrelationship. This is in contrast to so-called model-oriented specification in frameworks like VDM and Z, which consist of a simple realization of the required behaviour.

Specifications must be subject to a process of refinement (the filling-in of implementation detail) before they can actually be implemented. The result of such a refinement process is an executable algorithm, which is either formulated in a programming language, or in an executable subset of the specification language at hand. For example, Hartmann pipelines, when properly applied, may be considered a dataflow specification which is directly executable. Another example is the Actor model which has no specific application content and must be specialized to be executable.