2. Translators
A program which converts a user’s program
written in some language to another
language.
The language in which the user’s program is
written is called the source language
The language to which the source language
is converted is called the target language
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3. Translators
There is an important difference between
translation and interpretation. In the former,
the original program is first converted to an
equivalent program called an object program.
Then this object program is executed i.e. only
after the translation has been completed.
Hence, the original program in the source
language is not directly executed.
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4. Translators
translation comprises of two steps i.e
Generation of an equivalent program in
target language
Execution of the generated program
Interpretation consists of only one step i.e.
executing the original source program
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8. Phases in a compiler
Lexical analysis
Syntactic analysis
Semantic analysis
Intermediate code generation
Code optimization
Code generation
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9. Compiler
Compiler (Front - End )
Largely dependent on the source language
Independent of the target machine
Comprises the first three phases viz.,
– Lexical Analysis
– Syntactic Analysis
– Semantic Analysis
Sometimes the intermediate code
generation phase is also included
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10. Compiler
Back-End
Dependent on the target machine
Independent of the source language
Includes the last two phases viz.,
– Code Optimization
– Code Generation
5/1/2006 Computer System Software CS 012 BE 7th Semester 10
11. Lexical Analysis
Scans the source program into basic
elements called tokens
Prepares the symbol table which
maintains information about tokens
Eliminates white space characters such
as comments, blanks and tabs
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12. Lexical Analysis
EXAMPLE:
IF ( x < 5.0 ) THEN x=x+2 ELSE x=x-3;
TOKENS:
Keywords : IF, THEN, ELSE
Identifier(s) : x
Constants : 2, 3, 5.0
The blanks separating these tokens would
normally be eliminated during lexical analysis.
Nowadays, there are tools to do this phase
efficiently. For e.g. in Unix systems, a standard
tool called lex is available for this purpose.
5/1/2006 Computer System Software CS 012 BE 7th Semester 12
13. Syntax Analysis
Syntax analysis is also known as parsing or
hierarchical analysis.
It basically involves grouping of the
statements into grammatical phrases that are
used by the compiler to generate the output
finally. The grammatical phrases of the
source program are usually represented by a
parse tree( A parse tree is a structural
representation of the input being parsed) as
shown
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14. 5/1/2006 Computer System Software CS 012 BE 7th Semester 14
15. Syntax Analysis
there are tools to generate parsers. For
e.g. in Unix systems, a tool called as
YACC (Yet Another Compiler Compiler)
is available for this purpose.
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16. Semantic Analysis
Looks into the static meaning of the program
Gathers type information for the subsequent
code generation phase
Checks whether the type of variables used in
the program is consistent with the type
defined in the declaration.
Example: If a variable is defined as type char,
then it is not permitted to do arithmetic
operations on that variable.
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17. Intermediate Code Generation
Some compilers generate an explicit
intermediate representation of the source
program after syntax and semantic analysis.
This intermediate representation of the
source program can be thought of as a
program for an abstract machine and should
have two main properties viz.,
It should be easy to produce
It should be easy to translate into the target
program
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18. Next Session
Compilers -:
Code optimization
Code Generation
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