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4. Lexer and Parser Definition

The lexical analyzer defines how the contents of a file are broken into tokens, which is the basis for supporting custom language features. The easiest way to create a lexer is to use JFlex.

Reference: Implementing Lexer

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Required Project Configuration Change

The previous tutorial step Grammar and Parser, and this page, generate source files in the directory src/main/gen. To include those files, the project's sourceSets must be expanded by inserting the following line in the project's build.gradle file:

  sourceSets.main.java.srcDirs 'src/main/gen'

Or the following line in the project's build.gradle.kts file: 

  sourceSets["main"].java.srcDirs("src/main/gen")

4.1. Define a Lexer

Define a Simple.flex file with rules for the Simple Language lexer, as demonstrated in org.intellij.sdk.language.Simple.flex.

{% include /code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/Simple.flex %}

4.2. Generate a Lexer Class

Now generate a lexer class via JFlex Generator from the context menu on Simple.flex file.

The Grammar-Kit plugin uses the JFlex lexer generation. When running for the first time, JFlex prompts for a destination folder to download the JFlex library and skeleton. Choose the project root directory, for example code_samples/simple_language_plugin.

After that, the IDE generates the lexer under the gen directory, for example in simple_language_plugin/src/main/gen/org/intellij/sdk/language/SimpleLexer.

TIP Gradle plugin gradle-grammarkit-plugin can be used alternatively.

See Implementing Lexer for more information about using JFlex with the Consulo.

4.3. Define a Lexer Adapter

The JFlex lexer needs to be adapted to the Consulo Lexer API. This is done by subclassing FlexAdapter.

{% include /code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleLexerAdapter.java %}

4.4. Define a Root File

The SimpleFile implementation is the top-level node of the tree of PsiElements for a Simple Language file.

{% include /code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/psi/SimpleFile.java %}

4.5. Define a Parser

The Simple Language parser is defined by subclassing ParserDefinition.

{% include /code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleParserDefinition.java %}

4.6. Register the Parser Definition

Registering the parser definition in the plugin.xml file makes it available to the Consulo. Use the com.intellij.lang.parserDefinition extension point for registration. For example, see simple_language_plugin/src/main/resources/META-INF/plugin.xml.

  <extensions defaultExtensionNs="com.intellij">
    <lang.parserDefinition language="Simple"
            implementationClass="org.intellij.sdk.language.SimpleParserDefinition"/>
  </extensions>

4.7. Run the Project

With the simple_language_plugin loaded in a Development Instance, create a test.simple properties file with the following content:

# You are reading the ".properties" entry.
! The exclamation mark can also mark text as comments.
website = https://en.wikipedia.org/
language = English
# The backslash below tells the application to continue reading
# the value onto the next line.
message = Welcome to \
          Wikipedia!
# Add spaces to the key
key\ with\ spaces = This is the value that could be looked up with the key "key with spaces".
# Unicode
tab : \u0009

Now open the PsiViewer tool window and check how the lexer breaks the content of the file into tokens, and the parser parsed the tokens into PSI elements.

PSI Elements