Explain Pure and impure interpreters

In a pure interpreter, the source program is retained into the source form all throughout its interpretation. These arrangements incur substantial analysis overheads whereas interpreting a statement. In an impure interpreter performs several preliminary processing of the source program to decrease the analysis overheads throughout interpretation. The preprocessor changes the program to an intermediate representation (IR) that is used throughout interpretation. It speeds up interpretation as the code element of the IR that is the IC, can be analyzed extra efficiently than the source form of the program.