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ARCHITECTURE.md

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Here is a high-level overview of Language::Bel's architecture:

bin/bel, test suite, globals generator
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         Bel (the evalutaor)
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      Reader, Printer, Globals
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     Pair extensions, Primitives
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                Core

From the bottom up:

  • Language::Bel::Core contains all four basic data types, and the operations that act on them. These used to be spread out in different module files, but it was soon realized that they were all imported together, and belong together.
  • "Pair extensions" are an open set of types which extend normal pairs, such as numbers, strings, and lists of characters. Their reason for existing is usually to speed things up while at the same time maintaining the illusion that nothing is different. They all reside under the Language::Bel::Pair namespace.
  • Language::Bel::Primitives contains all the primitive function in Bel, those that are defined in terms of host language code instead of Bel code.
  • Language::Bel::Reader defines the reader in Perl. It will eventually go away, to be replaced by a call to read in Bel itself.
  • Language::Bel::Printer defines the printer in Perl. It will eventually go away, to be replaced by a call to print in Bel itself.
  • Language::Bel::Globals is full of definitions that populate the global environment when Bel starts up. It might not ever go away, but maybe one dares hope that it could be smaller.
  • The Bel evaluator, Language::Bel, uses most or all of the layers below, directly or indirectly. It will eventually go away, to be replaced by a call to bel in Bel itself.
  • Finally, on the top level, three clients that use the Bel evaluator:
    • The script bin/bel that runs a Bel REPL or a Bel source file.
    • The test suite in t, mostly powered by Language::Bel::Test and Language::Bel::Test::DSL.
    • The module Language::Bel::Globals::Generator, whose job it is to re-generate the global definitions now and then.