Assistance with Scala 3 metaprogramming
Hyperbole is a nascent set of tools to make it easier to write macros in Scala.
To begin, it includes an introspect
method which can provide useful
reflection detail about how the source of an expression translates into an AST.
- See a full introspection of an expression's AST
- Renders the AST structure in an easy-to-read tree format
- View source code alongside the AST
- Also view the "expanded" source code alongside, showing "invisible" syntax
- Produces output at compiletime or runtime, invoked inside or outside of a macro
Hyperbole runs at compiletime to inspect an expression, but can present its output in different ways:
- as a message reported at compiletime
- as a terminal compile error
- as a value which can be used in some way at runtime
It can be invoked on an expression in ordinary code, or in an inline context
where a Quotes
instance is available, on a lifted Expr
or a Tree
value.
In all cases, the macro is invoked with an introspect
method, either passing
the expression to be inspected, or a lifted Expr
expression value in a quoted
context, disambiguated by overloading. In a quoted context, an additional
optional parameter, terminate
, may be specified as true
to indicate that
the output should be reported as a compiler error rather than an informational
message at compiletime; by default it is false
.
A contextual Introspection
value determines what result should be yielded
from a call to introspect
. This given value can determine not only the result
type, but whether the expression is evaluated or its value retained. Three
implementations offered:
introspection.println
—records the introspection details tostdout
withprintln
, and returns the expression valueintrospection.text
—constructs aText
value containing the introspection details, ignoring the expression without evaluating it
The default is to log using Eucalyptus. Note that this contextual value is not
necessary for the introspect
method that take an Expr
value.
For example, in a macro method body,
import hyperbole.*
def macroImpl(expr: Expr[T])(using Quotes): Expr[Unit] =
import quotes.reflect.*
introspect(expr, terminate = true)
or, for example, in a Probably test,
import hyperbole.*, introspection.log
import probably.*
import eucalyptus.*, logging.stdout
test(t"Two joined lists are not empty"):
val xs = List(1)
val ys = List(2)
introspect(xs ++ ys)
.assert(!_.isEmpty)
Hyperbole is classified as embryonic. For reference, Soundness projects are categorized into one of the following five stability levels:
- embryonic: for experimental or demonstrative purposes only, without any guarantees of longevity
- fledgling: of proven utility, seeking contributions, but liable to significant redesigns
- maturescent: major design decisions broady settled, seeking probatory adoption and refinement
- dependable: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version
1.0.0
or later - adamantine: proven, reliable and production-ready, with no further breaking changes ever anticipated
Projects at any stability level, even embryonic projects, can still be used, as long as caution is taken to avoid a mismatch between the project's stability level and the required stability and maintainability of your own project.
Hyperbole is designed to be small. Its entire source code currently consists of 79 lines of code.
Hyperbole will ultimately be built by Fury, when it is published. In the meantime, two possibilities are offered, however they are acknowledged to be fragile, inadequately tested, and unsuitable for anything more than experimentation. They are provided only for the necessity of providing some answer to the question, "how can I try Hyperbole?".
-
Copy the sources into your own project
Read the
fury
file in the repository root to understand Hyperbole's build structure, dependencies and source location; the file format should be short and quite intuitive. Copy the sources into a source directory in your own project, then repeat (recursively) for each of the dependencies.The sources are compiled against the latest nightly release of Scala 3. There should be no problem to compile the project together with all of its dependencies in a single compilation.
-
Build with Wrath
Wrath is a bootstrapping script for building Hyperbole and other projects in the absence of a fully-featured build tool. It is designed to read the
fury
file in the project directory, and produce a collection of JAR files which can be added to a classpath, by compiling the project and all of its dependencies, including the Scala compiler itself.Download the latest version of
wrath
, make it executable, and add it to your path, for example by copying it to/usr/local/bin/
.Clone this repository inside an empty directory, so that the build can safely make clones of repositories it depends on as peers of
hyperbole
. Runwrath -F
in the repository root. This will download and compile the latest version of Scala, as well as all of Hyperbole's dependencies.If the build was successful, the compiled JAR files can be found in the
.wrath/dist
directory.
Contributors to Hyperbole are welcome and encouraged. New contributors may like to look for issues marked beginner.
We suggest that all contributors read the Contributing Guide to make the process of contributing to Hyperbole easier.
Please do not contact project maintainers privately with questions unless there is a good reason to keep them private. While it can be tempting to repsond to such questions, private answers cannot be shared with a wider audience, and it can result in duplication of effort.
Hyperbole was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.
Hyperbole is a tool for working with macros (short for macroinstructions) whose name implies a large—or hyperbolic—size.
In general, Soundness project names are always chosen with some rationale, however it is usually frivolous. Each name is chosen for more for its uniqueness and intrigue than its concision or catchiness, and there is no bias towards names with positive or "nice" meanings—since many of the libraries perform some quite unpleasant tasks.
Names should be English words, though many are obscure or archaic, and it should be noted how willingly English adopts foreign words. Names are generally of Greek or Latin origin, and have often arrived in English via a romance language.
The logo shows a set of shapes formed from hyperbolic curves, reminiscent of a butterfly.
Hyperbole is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.