Caesura

Simple parsing of CSV into case classes

Caesura provides an API for reading and writing CSV and TSV.

Features

• parse CSV and TSV data
• serialize product-like data (e.g. tuples or case classes) to CSV/TSV rows
• typeclass-based serialization and deserialization
• generic derivation of typeclasses for product and coproduct types

Availability

Getting Started

Reading CSV Data

CSV data can be read from any value whose type has a Source typeclass instance in scope, such as Text or a File from Galilei, passing it to the Csv.parse method. For example,

import caesura.*
import galilei.*
val file: File = ...
val csv: Csv = Csv.parse(file)

Likewise, TSV data can be read with:

import caesura.*
import galilei.*
val file: File = ...
val tsv: Tsv = Tsv.parse(file)

Row, Csv and Tsv Types

Both Csv and Tsv values are nothing more than wrappers around a sequence of Row instances, which are themselves IArrays of Text values. While Row instances are the same regardless of whether their purpose is for CSV or TSV data, when wrapped in a Csv or Tsv instance, they become serializable with the appropriate column separator (',' or '\t') and escaping.

Indeed, the companion objects Csv and Tsv are just two instances of the RowFormat type with different separator values and implementations of the RowFormat#escape method, and alternative formats may be created by subclassing RowFormat and overriding parameters.

Interpreting rows

A Row instance may be converted to a case class by calling its Row#as method with a target type parameter, for example,

val row: Row = Csv.parseRow(t"Richard,Smith,38")

case class Person(firstName: Text, lastName, Text, age: Int)
val person: Person = row.as[Person]

will instantiate an instance of Person, Person("Richard", "Smith", 38) by associating the positional fields in the case class definition with those in the Row, and applying the appropriate conversions to construct parameters of the appropriate types to instantiate the Person. In this example, the age field is parsed to construct an Int.

If a case class definition includes a nested case class, for example,

case class Person(firstName: Text, lastName: Text, age: Int)
case class Role(title: Text, person: Person, managerial: Boolean)

then the structure would first be flattened, so the order of the positional fields for the Role case class would be, title (0), person.firstName (1), person.lastName (2), person.age (3), and managerial (4).

This means the mapping from rows to case class instances is brittle: an additional field in a nested case class would be certain to break interpretation of rows. But that is unfortunately the nature of working with CSV.

The as method also exists on Csv and Tsv, and will return a List of values of the specified type.

Serializing to rows

Csv and Tsv instances may also be serialized to streams of data. Any Seq[T] (e.g. List[T] or LazyList[T]) may be transformed to CSV or TSV by calling the csv or tsv extension methods on it. For example,

val persons: List[Person] =
  List(Person(t"Richard", t"Smith", 38), person2, person3)

val personsTsv: Tsv = persons.tsv

Status

Caesura is classified as fledgling. 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.

Caesura is designed to be small. Its entire source code currently consists of 196 lines of code.

Building

Caesura 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 Caesura?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Caesura'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.

2. Build with Wrath

   Wrath is a bootstrapping script for building Caesura 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 caesura. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Caesura's dependencies.

   If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributing

Contributors to Caesura 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 Caesura 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.

Author

Caesura was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

Name

A caesura is break or pause in a sentence, often indicated by a comma—the same symbol that is used to indicate breaks in a CSV file.

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.

Logo

The logo is a comma, the significant character for separating values in CSV files.

License

Caesura is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.