Theory Scala

(*:maxLineLen=78:*)

theory Scala
imports Base
begin

chapter ‹Isabelle/Scala systems programming \label{sec:scala}›

text ‹
  Isabelle/ML and Isabelle/Scala are the two main implementation languages of
  the Isabelle environment:

    ▪ Isabelle/ML is for ∗‹mathematics›, to develop tools within the context
    of symbolic logic, e.g.\ for constructing proofs or defining
    domain-specific formal languages. See the ∗‹Isabelle/Isar implementation
    manual› \<^cite>‹"isabelle-implementation"› for more details.

    ▪ Isabelle/Scala is for ∗‹physics›, to connect with the world of systems
    and services, including editors and IDE frameworks.

  There are various ways to access Isabelle/Scala modules and operations:

    ▪ Isabelle command-line tools (\secref{sec:scala-tools}) run in a separate
    Java process.

    ▪ Isabelle/ML antiquotations access Isabelle/Scala functions
    (\secref{sec:scala-functions}) via the PIDE protocol: execution happens
    within the running Java process underlying Isabelle/Scala.

    ▪ The ▩‹Console/Scala› plugin of Isabelle/jEdit \<^cite>‹"isabelle-jedit"›
    operates on the running Java application, using the Scala
    read-eval-print-loop (REPL).

  The main Isabelle/Scala/jEdit functionality is provided by
  🗏‹$ISABELLE_HOME/lib/classes/isabelle.jar›. Further underlying Scala and
  Java libraries are bundled with Isabelle, e.g.\ to access SQLite or
  PostgreSQL via JDBC.

  Add-on Isabelle components may augment the system environment by providing
  suitable configuration in \<^path>‹etc/settings› (GNU bash script). The
  shell function \<^bash_function>‹classpath› helps to write
  \<^path>‹etc/settings› in a portable manner: it refers to library ▩‹jar›
  files in standard POSIX path notation. On Windows, this is converted to
  native platform format, before invoking Java (\secref{sec:scala-tools}).

  ┉
  There is also an implicit build process for Isabelle/Scala/Java modules,
  based on \<^path>‹etc/build.props› within the component directory (see also
  \secref{sec:scala-build}). See 🗏‹$ISABELLE_HOME/src/Tools/Demo/README.md›
  for an example components with command-line tools in Isabelle/Scala.
›


section ‹Command-line tools \label{sec:scala-tools}›

subsection ‹Java Runtime Environment \label{sec:tool-java}›

text ‹
  The @{tool_def java} tool is a direct wrapper for the Java Runtime
  Environment, within the regular Isabelle settings environment
  (\secref{sec:settings}) and Isabelle classpath. The command line arguments
  are that of the bundled Java distribution: see option ▩‹-help› in
  particular.

  The ▩‹java› executable is taken from @{setting ISABELLE_JDK_HOME}, according
  to the standard directory layout for regular distributions of OpenJDK.

  The shell function \<^bash_function>‹isabelle_jdk› allows shell scripts to
  invoke other Java tools robustly (e.g.\ ▩‹isabelle_jdk jar›), without
  depending on accidental operating system installations.
›


subsection ‹Scala toplevel \label{sec:tool-scala}›

text ‹
  The @{tool_def scala} tool is a direct wrapper for the Scala toplevel,
  similar to @{tool java} above. The command line arguments are that of the
  bundled Scala distribution: see option ▩‹-help› in particular. This allows
  to interact with Isabelle/Scala interactively.
›

subsubsection ‹Example›

text ‹
  Explore the Isabelle system environment in Scala:
  @{verbatim [display, indent = 2] ‹$ isabelle scala›}
  @{scala [display, indent = 2]
‹import isabelle._

val isabelle_home = Isabelle_System.getenv("ISABELLE_HOME")

val options = Options.init()
options.bool("browser_info")
options.string("document")›}
›


subsection ‹Scala compiler \label{sec:tool-scalac}›

text ‹
  The @{tool_def scalac} tool is a direct wrapper for the Scala compiler; see
  also @{tool scala} above. The command line arguments are that of the
  bundled Scala distribution.

  This provides a low-level mechanism to compile further Scala modules,
  depending on existing Isabelle/Scala functionality; the resulting ▩‹class›
  or ▩‹jar› files can be added to the Java classpath using the shell function
  \<^bash_function>‹classpath›.

  A more convenient high-level approach works via \<^path>‹etc/build.props›
  (see \secref{sec:scala-build}).
›


section ‹Isabelle/Scala/Java modules \label{sec:scala-build}›

subsection ‹Component configuration via \<^path>‹etc/build.props››

text ‹
  Isabelle components may augment the Isabelle/Scala/Java environment
  declaratively via properties given in \<^path>‹etc/build.props› (within the
  component directory). This specifies an output ▩‹jar› ∗‹module›, based on
  Scala or Java ∗‹sources›, and arbitrary ∗‹resources›. Moreover, a module can
  specify ∗‹services› that are subclasses of
  \<^scala_type>‹isabelle.Isabelle_System.Service›; these have a particular
  meaning to Isabelle/Scala tools.

  Before running a Scala or Java process, the Isabelle system implicitly
  ensures that all provided modules are compiled and packaged (as jars). It is
  also possible to invoke @{tool scala_build} explicitly, with extra options.

  ┉
  The syntax of \<^path>‹etc/build.props› follows a regular Java properties
  file⁋‹🌐‹https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/Properties.html#load(java.io.Reader)››,
  but the encoding is ▩‹UTF-8›, instead of historic ▩‹ISO 8859-1› from the API
  documentation.

  The subsequent properties are relevant for the Scala/Java build process.
  Most properties are optional: the default is an empty string (or list). File
  names are relative to the main component directory and may refer to Isabelle
  settings variables (e.g. ▩‹$ISABELLE_HOME›).

    ▪ ▩‹title› (required) is a human-readable description of the module, used
    in printed messages.

    ▪ ▩‹module› specifies a ▩‹jar› file name for the output module, as result
    of the specified sources (and resources). If this is absent (or
    ▩‹no_build› is set, as described below), there is no implicit build
    process. The contributing sources might be given nonetheless, notably for
    @{tool scala_project} (\secref{sec:tool-scala-project}), which includes
    Scala/Java sources of components, while suppressing ▩‹jar› modules (to
    avoid duplication of program content).

    ▪ ▩‹no_build› is a Boolean property, with default ▩‹false›. If set to
    ▩‹true›, the implicit build process for the given ▩‹module› is ∗‹omitted›
    --- it is assumed to be provided by other means.

    ▪ ▩‹scalac_options› and ▩‹javac_options› augment the default settings
    @{setting_ref ISABELLE_SCALAC_OPTIONS} and @{setting_ref
    ISABELLE_JAVAC_OPTIONS} for this component; option syntax follows the
    regular command-line tools ▩‹scalac› and ▩‹javac›, respectively.

    ▪ ▩‹main› specifies the main entry point for the ▩‹jar› module. This is
    only relevant for direct invocation like ``▩‹java -jar test.jar›''.

    ▪ ▩‹requirements› is a list of ▩‹jar› modules that are needed in the
    compilation process, but not provided by the regular classpath (notably
    @{setting ISABELLE_CLASSPATH}).

    A ∗‹normal entry› refers to a single ▩‹jar› file name, possibly with
    settings variables as usual. E.g. 🗏‹$ISABELLE_SCALA_JAR› for the main
    🗏‹$ISABELLE_HOME/lib/classes/isabelle.jar› (especially relevant for
    add-on modules).

    A ∗‹special entry› is of the form ▩‹env:›‹variable› and refers to a
    settings variable from the Isabelle environment: its value may consist of
    multiple ▩‹jar› entries (separated by colons). Environment variables are
    not expanded recursively.

    ▪ ▩‹resources› is a list of files that should be included in the resulting
    ▩‹jar› file. Each item consists of a pair separated by colon:
    ‹source›▩‹:›‹target› means to copy an existing source file (relative to
    the component directory) to the given target file or directory (relative
    to the ▩‹jar› name space). A ‹file› specification without colon
    abbreviates ‹file›▩‹:›‹file›, i.e. the file is copied while retaining its
    relative path name.

    ▪ ▩‹sources› is a list of ▩‹.scala› or ▩‹.java› files that contribute to
    the specified module. It is possible to use both languages simultaneously:
    the Scala and Java compiler will be invoked consecutively to make this
    work.

    ▪ ▩‹services› is a list of class names to be registered as Isabelle
    service providers (subclasses of
    \<^scala_type>‹isabelle.Isabelle_System.Service›). Internal class names of
    the underlying JVM need to be given: e.g. see method @{scala_method (in
    java.lang.Object) getClass}.

    Particular services require particular subclasses: instances are filtered
    according to their dynamic type. For example, class
    \<^scala_type>‹isabelle.Isabelle_Scala_Tools› collects Scala command-line
    tools, and class \<^scala_type>‹isabelle.Scala.Functions› collects Scala
    functions (\secref{sec:scala-functions}).
›


subsection ‹Explicit Isabelle/Scala/Java build \label{sec:tool-scala-build}›

text ‹
  The @{tool_def scala_build} tool explicitly invokes the build process for
  all registered components.
  @{verbatim [display]
‹Usage: isabelle scala_build [OPTIONS]

  Options are:
    -f           force fresh build
    -q           quiet mode: suppress stdout/stderr

  Build Isabelle/Scala/Java modules of all registered components
  (if required).
›}

  For each registered Isabelle component that provides
  \<^path>‹etc/build.props›, the specified output ▩‹module› is checked against
  the corresponding input ▩‹requirements›, ▩‹resources›, ▩‹sources›. If
  required, there is an automatic build using ▩‹scalac› or ▩‹javac› (or both).
  The identity of input files is recorded within the output ▩‹jar›, using SHA1
  digests in ▩‹META-INF/isabelle/shasum›.

  ┉
  Option ▩‹-f› forces a fresh build, regardless of the up-to-date status of
  input files vs. the output module.

  ┉
  Option ▩‹-q› suppresses all output on stdout/stderr produced by the Scala or
  Java compiler.

  ┉ Explicit invocation of @{tool scala_build} mainly serves testing or
  applications with special options: the Isabelle system normally does an
  automatic the build on demand.
›


subsection ‹Project setup for common Scala IDEs \label{sec:tool-scala-project}›

text ‹
  The @{tool_def scala_project} tool creates a project configuration for all
  Isabelle/Java/Scala modules specified in components via
  \<^path>‹etc/build.props›, together with additional source files given on
  the command-line:

  @{verbatim [display]
‹Usage: isabelle scala_project [OPTIONS] [MORE_SOURCES ...]

  Options are:
    -D DIR       project directory (default: "$ISABELLE_HOME_USER/scala_project")
    -G           use Gradle as build tool
    -L           make symlinks to original source files
    -M           use Maven as build tool
    -f           force update of existing directory

  Setup project for Isabelle/Scala/jEdit --- to support common IDEs such
  as IntelliJ IDEA. Either option -G or -M is mandatory to specify the
  build tool.›}

  The generated configuration is for Gradle⁋‹🌐‹https://gradle.org›› or
  Maven⁋‹🌐‹https://maven.apache.org››, but the main purpose is to import it
  into common IDEs like IntelliJ IDEA⁋‹🌐‹https://www.jetbrains.com/idea››.
  This allows to explore the sources with static analysis and other hints in
  real-time.

  The generated files refer to physical file-system locations, using the path
  notation of the underlying OS platform. Thus the project needs to be
  recreated whenever the Isabelle installation is changed or moved.

  ┉
  Option ▩‹-G› selects Gradle and ▩‹-M› selects Maven as Java/Scala build
  tool: either one needs to be specified explicitly. These tools have a
  tendency to break down unexpectedly, so supporting both increases the
  chances that the generated IDE project works properly.

  ┉
  Option ▩‹-L› produces ∗‹symlinks› to the original files: this allows to
  develop Isabelle/Scala/jEdit modules within an external IDE. The default is
  to ∗‹copy› source files, so editing them within the IDE has no permanent
  effect on the originals.

  ┉
  Option ▩‹-D› specifies an explicit project directory, instead of the default
  \<^path>‹$ISABELLE_HOME_USER/scala_project›. Option ▩‹-f› forces an existing
  project directory to be ∗‹purged› --- after some sanity checks that it has
  been generated by @{tool "scala_project"} before.
›


subsubsection ‹Examples›

text ‹
  Create a project directory and for editing the original sources:

  @{verbatim [display] ‹isabelle scala_project -f -L›}

  On Windows, this usually requires Administrator rights, in order to create
  native symlinks.
›


section ‹Registered Isabelle/Scala functions \label{sec:scala-functions}›

subsection ‹Defining functions in Isabelle/Scala›

text ‹
  The service class \<^scala_type>‹isabelle.Scala.Functions› collects Scala
  functions of type \<^scala_type>‹isabelle.Scala.Fun›: by registering
  instances via ▩‹services› in \<^path>‹etc/build.props›
  (\secref{sec:scala-build}), it becomes possible to invoke Isabelle/Scala
  from Isabelle/ML (see below).

  An example is the predefined collection of
  \<^scala_type>‹isabelle.Scala.Functions› in
  🗏‹$ISABELLE_HOME/etc/build.props›. The overall list of registered functions
  is accessible in Isabelle/Scala as
  \<^scala_object>‹isabelle.Scala.functions›.

  The general class \<^scala_type>‹isabelle.Scala.Fun› expects a multi-argument
  / multi-result function
  \<^scala_type>‹List[isabelle.Bytes] => List[isabelle.Bytes]›; more common are
  instances of \<^scala_type>‹isabelle.Scala.Fun_Strings› for type
  \<^scala_type>‹List[String] => List[String]›, or
  \<^scala_type>‹isabelle.Scala.Fun_String› for type
  \<^scala_type>‹String => String›.
›


subsection ‹Invoking functions in Isabelle/ML›

text ‹
  Isabelle/PIDE provides a protocol to invoke registered Scala functions in
  ML: this works both within the Prover IDE and in batch builds.

  The subsequent ML antiquotations refer to Scala functions in a
  formally-checked manner.

  \begin{matharray}{rcl}
  @{ML_antiquotation_def "scala_function"} & : & ‹ML_antiquotation› \\
  @{ML_antiquotation_def "scala"} & : & ‹ML_antiquotation› \\
  \end{matharray}

  \<^rail>‹
    (@{ML_antiquotation scala_function} |
     @{ML_antiquotation scala}) @{syntax embedded}
  ›

  ➧ ‹@{scala_function name}› inlines the checked function name as ML string
    literal.

  ➧ ‹@{scala name}› and ‹@{scala_thread name}› invoke the checked function via
  the PIDE protocol. In Isabelle/ML this appears as a function of type
  \<^ML_type>‹string list -> string list› or \<^ML_type>‹string -> string›,
  depending on the definition in Isabelle/Scala. Evaluation is subject to
  interrupts within the ML runtime environment as usual. A \<^scala>‹null›
  result in Scala raises an exception \<^ML>‹Scala.Null› in ML. The execution
  of ‹@{scala}› works via a Scala future on a bounded thread farm, while
  ‹@{scala_thread}› always forks a separate Java/VM thread.

  The standard approach of representing datatypes via strings works via XML in
  YXML transfer syntax. See Isabelle/ML operations and modules @{ML
  YXML.string_of_body}, @{ML YXML.parse_body}, @{ML_structure XML.Encode},
  @{ML_structure XML.Decode}; similarly for Isabelle/Scala. Isabelle symbols
  may have to be recoded via Scala operations
  \<^scala_method>‹isabelle.Symbol.decode› and
  \<^scala_method>‹isabelle.Symbol.encode›.
›


subsubsection ‹Examples›

text ‹
  Invoke the predefined Scala function \<^scala_function>‹echo›:
›

ML ‹
  val s = "test";
  val s' = \<^scala>‹echo› s;
  \<^assert> (s = s')
›

text ‹
  Let the Scala compiler process some toplevel declarations, producing a list
  of errors:
›

ML ‹
  val source = "class A(a: Int, b: Boolean)"
  val errors =
    \<^scala>‹scala_toplevel› source
    |> YXML.parse_body
    |> let open XML.Decode in list string end;

  \<^assert> (null errors)›

text ‹
  The above is merely for demonstration. See \<^ML>‹Scala_Compiler.toplevel›
  for a more convenient version with builtin decoding and treatment of errors.
›


section ‹Documenting Isabelle/Scala entities›

text ‹
  The subsequent document antiquotations help to document Isabelle/Scala
  entities, with formal checking of names against the Isabelle classpath.

  \begin{matharray}{rcl}
  @{antiquotation_def "scala"} & : & ‹antiquotation› \\
  @{antiquotation_def "scala_object"} & : & ‹antiquotation› \\
  @{antiquotation_def "scala_type"} & : & ‹antiquotation› \\
  @{antiquotation_def "scala_method"} & : & ‹antiquotation› \\
  \end{matharray}

  \<^rail>‹
    (@@{antiquotation scala} | @@{antiquotation scala_object})
      @{syntax embedded}
    ;
    @@{antiquotation scala_type} @{syntax embedded} types
    ;
    @@{antiquotation scala_method} class @{syntax embedded} types args
    ;
    class: ('(' @'in' @{syntax name} types ')')?
    ;
    types: ('[' (@{syntax name} ',' +) ']')?
    ;
    args: ('(' (nat | (('_' | @{syntax name}) + ',')) ')')?
  ›

  ➧ ‹@{scala s}› is similar to ‹@{verbatim s}›, but the given source text is
  checked by the Scala compiler as toplevel declaration (without evaluation).
  This allows to write Isabelle/Scala examples that are statically checked.

  ➧ ‹@{scala_object x}› checks the given Scala object name (simple value or
  ground module) and prints the result verbatim.

  ➧ ‹@{scala_type T[A]}› checks the given Scala type name (with optional type
  parameters) and prints the result verbatim.

  ➧ ‹@{scala_method (in c[A]) m[B](n)}› checks the given Scala method ‹m› in
  the context of class ‹c›. The method argument slots are either specified by
  a number ‹n› or by a list of (optional) argument types; this may refer to
  type variables specified for the class or method: ‹A› or ‹B› above.

  Everything except for the method name ‹m› is optional. The absence of the
  class context means that this is a static method. The absence of arguments
  with types means that the method can be determined uniquely as ▩‹(›‹m›▩‹ _)›
  in Scala (no overloading).
›


subsubsection ‹Examples›

text ‹
  Miscellaneous Isabelle/Scala entities:

    ▪ object: \<^scala_object>‹isabelle.Isabelle_Process›
    ▪ type without parameter: @{scala_type isabelle.Console_Progress}
    ▪ type with parameter: @{scala_type List[A]}
    ▪ static method: \<^scala_method>‹isabelle.Isabelle_System.bash›
    ▪ class and method with type parameters:
      @{scala_method (in List[A]) map[B]("A => B")}
    ▪ overloaded method with argument type: @{scala_method (in Int) "+" (Int)}
›

end