What are the stages of interpreting a programming language?

The stages of interpreting a programming language are lexical analysis, syntax analysis, semantic analysis, and execution.

The first stage in interpreting a programming language is lexical analysis. This is where the source code is broken down into smaller pieces, known as tokens. Tokens are the basic building blocks of a program, representing individual elements such as keywords, identifiers, operators, and punctuation. The lexical analyser, or lexer, reads the source code character by character, grouping them into tokens based on a set of predefined rules. This process also involves removing white spaces and comments, and checking for lexical errors such as invalid characters or identifiers.

The next stage is syntax analysis, also known as parsing. The parser takes the tokens produced by the lexer and arranges them into a hierarchical structure that represents the grammatical structure of the program, typically in the form of a parse tree or syntax tree. This stage checks for syntax errors, such as missing parentheses or mismatched brackets. The syntax rules are defined by the grammar of the programming language, which specifies how tokens can be combined to form valid statements and expressions.

Following syntax analysis is semantic analysis. This stage involves checking the program for semantic errors, which are errors in the meaning or logic of the program. The semantic analyser checks that the operations are being performed on compatible data types, that variables are declared before they are used, that functions are called with the correct number and type of arguments, and so on. It may also perform type checking, and convert the syntax tree into an intermediate representation that is easier for the interpreter to execute.

The final stage is execution. The interpreter executes the program directly from the intermediate representation or the syntax tree, statement by statement. It performs the operations specified by the program, such as arithmetic calculations, input/output operations, control flow operations, and so on. The interpreter also manages the program's runtime environment, keeping track of variable values, memory allocation, and function calls. If any runtime errors occur, such as division by zero or out-of-bounds array access, the interpreter halts execution and reports the error.