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As you have probably guessed from the section title, the processing of DSL's proceeds exactly as for general purpose languages.The lexical analysis splits the text based on the special characters: I find it helpful to think of the AST as the in-memory representation of the instructions for the next processing step.Back then, it was practically unheard of to do this.
It turns out that there are fundamental similarities between the old and new versions "code generation, and comparing them helps us understand the similarities.
It is a good place to start to understand today's code generation landscape.
A regular expression is a series of commands to find a substring of a larger string based on its shape rather than the exact text - so it was pattern matching for text.
A regular expression is made up of a number of actions - basically telling the interpreter what to do to find the string.
At that time, "machine" meant a CPU instruction set - so this was machine operation code being generated.
Having learnt all compiling languages like FORTRAN and PL/I, my second job - way before the PC, let alone the dreaded CASE tools - was to build a code generator to create CRUD applications.
We're interested in code generators, but the regular expression handler in my editor is interpreted; the same AST works equally well.
Each node in the AST is an instance of a class, with qualifying attributes (e.g.
Something like this: (If you know regular expression, please forgive the conversion of '.*' into 'rest Of Line' - it would be strictly correct as a 'zero Or More' plus 'any Character' combination.) While lengthy regular expressions demand patience and humility to debug, in their domain (pattern-based text searching) they are sharper and faster than the general-purpose alternative.
This is characteristic of a good DSL: its conciseness aids thinking because there is a direct correspondence between how an expert thinks and the symbols of the DSL.
In thousands of lines, we often want to find where the initialization is finished for a particular run, so there is a line like: The '^' matches the beginning of the line and then the characters "21:" select the 9pm timeframe.