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Syntactic Analysis
Consider the following C++ function. There are a number of syntax errors present.
1. int* foo(int i, int j))
2. {
3. for(k=0; i j; )
4. fi( i > j )
5. return j;
6. }
Line 1 has extra parenthesis at the end. The boolean expression in the for loop in line 3 is
incorrect. Line 4 has a missing semicolon at the end. All such errors are due to the fact
the function does not abide by the syntax of the C++ language grammar.
Semantic Analysis
Consider the English language sentence “He wrote the computer”. The sentence is
syntactically correct but semantically wrong. The meaning of the sentence is incorrect;
one does not “write” a computer. Issues related to meaning fall under the heading of
semantic analysis. The following C++ function has semantic errors. The type of the local
variable sum has not been declared. The returned value does not match the return value
type of the function (int*). The function is syntactically correct.
int* foo(int i, int j)
{
for(k=0; i < j; j++ )
if( i < j-2 )
sum = sum+i
return sum;
}
Role of the Parser
Not all sequences of tokens are program. Parser must distinguish between valid and
invalid sequences of tokens. What we need is an expressive way to describe the syntax of
programs and an acceptor mechanism that determines if input token stream satisfies the
syntax of the programming language. The acceptor mechanism determines if input token
stream satisfies the syntax of a programming language.
Parsing is the process of discovering a derivation for some sentence of a language. The
mathematical model of syntax is represented by a grammar G. The language generated
