meta

Metaprogramming

• Subcontents
  • Make a programming language
• Goals
  • Write a metaprogram in Haskell to generate a Java 8 enterprise web application.
    • What we mean by "enterprise web application":
      • User uses web browser to interact with the application.
      • Lots of CRUD (Create, Read, Update, Delete).
      • Some business logic.
      • Used internally in a small company.
      • Less than 100 users.
    • What we don't mean by "enterprise web application":
      • Java Enterprise Edition (Java EE), except Servlet API.
  • Reverse-engineer an obfuscated Java 6 application.
    • Approach:
      • Transform Java bytecode into something related to lambda calculus.
      • Simplify (optimize) the representation.
      • Transform it back into Java bytecode.
  • Create an abstract programming language that can represent the semantics of all programming languages.
    • Use it to translate programs across programming languages.
    • Similar to Pandoc but for programming languages.
• Assumptions
  • The user of this library is programmer / developer / software engineer.
  • Small changes are more likely to be accepted and persisted than big changes.
• Directory structure
  • Non-generated files
    • src: Haskell source files
    • rt: runtimes
      • java: Java runtime
    • har: harness for running example application
      • the non-generated part of the examples
  • Generated files
    • src1: stage-1 Haskell source files
• Plans
  • Small changes that are likely to be accepted.
    • Generate Java entity class from PostgreSQL information_schema or DDL statements.
      • Decision:
        • Parse DDL statements, don't connect to database.
      • Choose:
        • Parse SQL DDL statements from a file (manually written, or dumped from database).
          • Pros:
            • More secure: The program doesn't need the database credentials.
          • Cons:
            • Need to write an SQL parser.
        • Connect to database.
          • Pros:
            • Doesn't need SQL DDL file.
              • But the DDL file can be generated easily from the database anyway ("dump schema" option).
          • Cons:
            • How standard is information_schema?
  • Add a type parameter to Query.
  • Pretty URL (URL path component instead of GET parameters)?
  • Refactoring, maintainability/usability improvements
    • Make Meta.Xml use Meta.WrapM
  • Absorb haji, pragmatic, ptt.
  • Do we want this?
    • change deploy script
      • build on developer machine
    • describe tables in Relat
    • CUD (create, update, delete) of CRUD
    • servlet: basic auth
    • dto: auto-jackson
    • dto: Api req/res Dto includes write and read to json using jackson core without databind; collect those static methods in 1 class
    • dto: Backend, Android, and iOS dto generation
    • java: compile-time design pattern (mixin, delegation, decorator)
      • requires reading java class to delegate all public instance methods
      • requires reading java source for mixin
    • derive web view from database table (from hs, not sql)
      • query description language Query, basically Linq
        • assume cross-server query ("federation")
          • https://en.wikipedia.org/wiki/Federated_database_system
          • assume different database servers
          • assume different database vendors
          • a Table must know its "location"/"type"/"source type"/"access method", to determine what code is generated to query it.
            • decide terminology: "source type"? "access method"? "source alias"?
              • Examples of access methods: postgresql, mysql, in-application.
            • how to access the table:
              • what code to generate for query
              • where the table is (where to connect to)
                • how to find out where to connect to
                  • hardcoded in the application
                  • read from file at runtime, not in version control
                  • by a variable passed by harness
          • assume that a data source is an Iterable<Object[]>?
            • Linq assumes that every table is a Sequence?
        • https://www.devart.com/dotconnect/postgresql/articles/tutorial_linq.html
      • view description language View
        • VAutoFromQuery :: Query -> View
      • try-with-resources: JavaSta, JavaRender
      • begin with dump all
      • then add pagination (offset, limit)
      • then add conjunctive-normal-form filter
    • fix auto-increment column ddl, limit to int16, int32, and int64 (smallserial, serial, bigserial)
    • embed lambda calculus in Query?
    • user experience
      • read from XML? YAML?
    • Generate XSD from Haskell record so that IDEA can autocomplete?
      • incorporate UUXML? But that's from XSD to Haskell. We want from Haskell to XSD.
        • http://wiki.di.uminho.pt/twiki/pub/Education/Archive/XMLtoSQLConversionToolAFPProject/padl04.pdf
    • Standardize C project build and layout?