Case-insensitive languages

Some programming languages such as SQL or Structured Text use case insensitivity to provide more flexibility when writing code. For example most SQL databases accept select statements starting with select, SELECT or even SeLeCt.

In case you want to provide your users the same flexibility with your language, there are different levels of case-insensitivity in Langium:

• You can make Langium’s parser completely case insensitive using the language configuration
• You can include case-insensitivity for specific terminal rules
• You can make cross references case insensitive

All of these options can be enabled independent of one another.

To make Langium case-insensitive, you have to set the caseInsensitive option to true in the LangiumConfig object which is located in the langium-config.json file at the root of your Langium project. You can set this up for every single language.

{
    ...
    "languages": [
      {
        "id": "hello-world",
        "caseInsensitive": true, // <-- makes the specified language case insensitive
        ...
      },
      ...
    ],
    ...
}

If you want to include case-insensitivity only where you need it, you can use the i flag inside of your grammar’s regular expressions

// append `i` to any regex to make it case insensitive
terminal ID: /[A-Z]/i;

Note that regular expressions can only be used inside of terminal rules.

But be aware of that both ways will only take care of all the keywords in your grammar. If you want identifiers and cross-references to be case-insensitive as well, you have to adjust your scoping for each cross-reference case. This can be accomplished by setting the caseInsensitive option to true within the options when you are creating a new scope object.

There are several implementations of scopes. MapScope is very commonly used:

new MapScope(descriptions, parentScope, { caseInsensitive: true });