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 🚫‹$ISABELLE_HOME/lib/classes/isabelle.jar›. Further underlying Scala and
Java libraries are bundled with Isabelle, e.g.\ to access SQLite or
PostgreSQL via JDBC.
Add-on Isabelle components may augment the system environment by providing
suitable configuration in 🚫‹etc/settings› (GNU bash script). The
shell function 🚫‹classpath› helps to write 🚫‹etc/settings› in a portable manner: it refers to library ▩‹jar›
files in standard POSIX path notation. On Windows, this is converted to
native platform format, before invoking Java (\secref{sec:scala-tools}).
┉
There is also an implicit build process for Isabelle/Scala/Java modules,
based on 🚫‹etc/build.props› within the component directory (see also \secref{sec:scala-build}). See 🚫‹$ISABELLE_HOME/src/Tools/Demo/README.md›
for an example components with command-line tools in Isabelle/Scala. ›
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 🚫‹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._
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 🚫‹classpath›.
A more convenient high-level approach works via 🚫‹etc/build.props›
(see \secref{sec:scala-build}). ›
subsection‹Component configuration via 🚫‹etc/build.props››
text‹
Isabelle components may augment the Isabelle/Scala/Java environment
declaratively via properties given in 🚫‹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 🚫‹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 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 🚫‹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 🚫‹isabelle.Isabelle_Scala_Tools› collects Scala command-line
tools, and class 🚫‹isabelle.Scala.Functions› collects Scala
functions (\secref{sec:scala-functions}). ›
text‹
The @{tool_def scala_build} tool explicitly invokes the build process for
all registered components.
@{verbatim [display] ‹Usage: isabelle scala_build [OPTIONS]
Build Isabelle/Scala/Java modules of all registered components
(if required). ›}
For each registered Isabelle component that provides 🚫‹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 🚫‹etc/build.props›, together with additional source files given on
the command-line:
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
-v verbose
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 🚫‹$ISABELLE_HOME_USER/scala_project›. Option ▩‹-f› forces an existing
project directory to be ∗‹purged› --- after some sanity checks that it has
been generated by @{tool "scala_project"} before.
┉
Option ▩‹-v› enables verbose mode. ›
subsubsection‹Examples›
text‹
Create a project directory and for editing the original sources:
text‹
The service class 🚫‹isabelle.Scala.Functions› collects Scala
functions of type 🚫‹isabelle.Scala.Fun›: by registering
instances via ▩‹services› in 🚫‹etc/build.props›
(\secref{sec:scala-build}), it becomes possible to invoke Isabelle/Scala
from Isabelle/ML (see below).
An example is the predefined collection of 🚫‹isabelle.Scala.Functions› in 🚫‹$ISABELLE_HOME/etc/build.props›. The overall list of registered functions
is accessible in Isabelle/Scala as 🚫‹isabelle.Scala.functions›.
The general class 🚫‹isabelle.Scala.Fun› expects a multi-argument
/ multi-result function 🚫‹List[isabelle.Bytes] => List[isabelle.Bytes]›; more common are
instances of 🚫‹isabelle.Scala.Fun_Strings› for type 🚫‹List[String] => List[String]›, or 🚫‹isabelle.Scala.Fun_String› for 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.
🚫‹@{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 🚫‹string list -> string list› or 🚫‹string -> string›,
depending on the definition in Isabelle/Scala. Evaluation is subject to
interrupts within the ML runtime environment as usual. A 🚫‹null›
result in Scala raises an exception 🚫‹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 🚫‹isabelle.Symbol.decode› and 🚫‹isabelle.Symbol.encode›. ›
subsubsection‹Examples›
text‹
Invoke the predefined Scala function 🚫‹echo›: ›
ML ‹
val s = "test";
val s' = 🚫‹echo› s; 🚫 (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_toplevel› source
|> YXML.parse_body
|> let open XML.Decode in list string end;
🚫 (null errors)›
text‹
The above is merely for demonstration. See 🚫‹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.
🚫‹@{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: 🚫‹isabelle.Isabelle_Process› ▪ type without parameter: @{scala_type isabelle.Console_Progress} ▪ type with parameter: @{scala_type List[A]} ▪ static 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
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