Resumen
Purpose-built languages sprout like weeds alongside the road of mainstream language development, and they exhibit properties and a history that lead one to reconsider instinctive answers to the fundamental language questions. Most significantly, purpose-built languages have often formed an essential part of the development of larger software systems such as operating systems, whether as a part of developer tools or as glue between distinct pieces of a larger environment. The Unix environment, with its philosophy of little tools that can be easily connected, was an ideal greenhouse for the growth of purpose-built languages. A cursory scan of Unix manuals from the early 1980s shows more than 20 little languages of various forms in active use. Mutation, some accidental and some intentional, often plays a critical role in the development of purpose-built systems languages. One common form of mutation involves adding a subset of the syntax of one language (for example, expressions or regular expressions) to another language