alleryStart learning →Which formalism is most commonly used to specify the LEXICAL structure of programming language tokens?
ATuring machines
BContext-free grammars
CRegular expressions
DPredicate logic
Answer & Solution
Correct answer: C. Regular expressions
1. Lexical structure is REGULAR: tokens like identifiers, numbers, keywords can be described by REGULAR EXPRESSIONS.
2. Regex → NFA → DFA. The DFA becomes the scanner table.
3. Tools like lex, flex, ANTLR use this exact pipeline.
4. Context-free grammars (option B) are used for SYNTAX (parser), not lexical analysis. Turing machines and predicate logic are far more powerful than needed for tokenisation.
_Source: Bob Nystrom, "Crafting Interpreters", Ch 4.3 (Regular Languages and Expressions)._
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