The blog post delves into extending an existing number format parser using the Ohm meta language to create a basic arithmetic calculator, eventually evolving it into a primitive programming language. The text explains the process of building a parser to handle arithmetic expressions by defining grammar rules and operator precedence, followed by implementing semantics for performing arithmetic operations. It introduces the concept of expression trees for deferred arithmetic evaluation, enabling more complex operations like function calls within loops. The post further discusses adding symbols, assignments, and a scope to manage variable values, thereby establishing the groundwork for more advanced language features such as conditionals and loops. The article emphasizes the importance of breaking down the language-building process into smaller, manageable steps and highlights the use of expression trees and symbol management as crucial elements for future language development.