char_reader

A Scala library for intelligent character-by-character reading with automatic indentation tracking.

Overview

char_reader provides a powerful abstraction for parsing text with significant whitespace. It automatically generates INDENT and DEDENT tokens when indentation levels change, making it ideal for parsing languages like Python, YAML, or any custom DSL that uses indentation for structure.

Key features include:

Automatic indentation tracking with configurable indentation styles
Precise position tracking (line and column numbers)
Cross-platform support (JVM, JavaScript via Scala.js, and Native)
Rich error reporting with contextual information
Flexible iteration over characters with lookahead capabilities
Comment line detection and handling

Installation

Add the dependency to your build.sbt:

libraryDependencies += "io.github.edadma" %%% "char_reader" % "0.1.25"

For cross-platform projects, use %%% to automatically select the appropriate artifact.

Basic Usage

Simple Character Reading

import io.github.edadma.char_reader.CharReader

// Read from string without indentation tracking
val reader = CharReader.fromString("Hello\nWorld")
while (!reader.eoi) {
  println(s"Char: '${reader.ch}' at line ${reader.line}, column ${reader.col}")
  reader = reader.next
}

Indentation-Aware Reading

import io.github.edadma.char_reader.CharReader

val text = """
|1
| a
|  b
| c
|2
""".stripMargin

// Configure comment syntax (prefix, middle, suffix)
val reader = CharReader.fromString(text, indentation = Some(("#", "", "")))

reader.iterator.foreach { r =>
  r.ch match {
    case CharReader.INDENT => println("Indentation increased")
    case CharReader.DEDENT => println("Indentation decreased")
    case CharReader.EOI    => println("End of input")
    case '\n'              => println("Newline")
    case c                 => println(s"Character: '$c'")
  }
}

Reading from File

val reader = CharReader.fromFile("input.txt", indentation = Some(("#", "", "")))

Advanced Features

Pattern Matching

val reader = CharReader.fromString("function hello() {")

reader.matches("function") match {
  case Some(nextReader) => println("Found 'function' keyword")
  case None => println("Pattern not found")
}

Consuming Text

// Consume until whitespace
val (consumed, rest) = reader.consume(_.ch.isWhitespace)
println(s"Consumed: '$consumed'")

// Consume past a delimiter
reader.consumePastDelimiter("*/") match {
  case Some((content, rest)) => println(s"Comment content: '$content'")
  case None => println("Delimiter not found")
}

Error Reporting

val reader = CharReader.fromString("error here")
reader.error("Unexpected token") // Throws with context

Output:

Unexpected token (line 1, column 1):
error here
^

Special Characters

CharReader.EOI: End of Input
CharReader.INDENT: Indentation level increased
CharReader.DEDENT: Indentation level decreased

Configuration

Tab Width

CharReader.fromString(text, tabs = 4) // Default tab width

Indentation Settings

// Configure comment syntax: (prefix, middle, suffix)
val pythonStyle = Some(("#", "", ""))
val cStyle = Some(("/*", "", "*/"))
val reader = CharReader.fromString(text, indentation = pythonStyle)

Building

This project uses SBT with cross-compilation:

# Test all platforms
sbt test

# Test specific platform
sbt charReaderJVM/test
sbt charReaderJS/test
sbt charReaderNative/test

# Publish
sbt publishSigned

License

ISC

edadma / char_reader 0.1.25