cddl

Basic Types

The CDDL AST parser defines several basic types that form the building blocks of the Abstract Syntax Tree. This document describes these core types.

Primitive Types

The parser supports the following primitive types as defined in the CDDL specification:

export enum Type {
    /**
     * any types
     */
    ANY = 'any',

    /**
     * boolean types
     */
    // Boolean value (major type 7, additional information 20 or 21).
    BOOL = 'bool',

    /**
     * numeric types
     */
    // An unsigned integer or a negative integer.
    INT = 'int',
    // An unsigned integer (major type 0).
    UINT = 'uint',
    // A negative integer (major type 1).
    NINT = 'nint',
    // One of float16, float32, or float64.
    FLOAT = 'float',
    // A number representable as an IEEE 754 half-precision float
    FLOAT16 = 'float16',
    // A number representable as an IEEE 754 single-precision
    FLOAT32 = 'float32',
    // A number representable as an IEEE 754 double-precision
    FLOAT64 = 'float64',

    /**
     * string types
     */
    // A byte string (major type 2).
    BSTR = 'bstr',
    // A byte string (major type 2).
    BYTES = 'bytes',
    // Text string (major type 3)
    TSTR = 'tstr',
    // Text string (major type 3)
    TEXT = 'text',

    /**
     * null types
     */
    NIL = 'nil',
    NULL = 'null'
}

These types correspond to the CBOR (Concise Binary Object Representation) types as specified in RFC 7049.

Type References

In the AST, a type reference can be represented in several ways:

1. As a string directly corresponding to one of the primitive types:

   "Type": "tstr"
   

2. As a property reference to another named type:

   "Type": {
     "Type": "group",
     "Value": "person",
     "Unwrapped": false
   }
   

3. As a literal value:

   "Type": {
     "Type": "literal",
     "Value": "some string",
     "Unwrapped": false
   }
   

4. As a range:

   "Type": {
     "Type": "range",
     "Value": {
       "Min": 0,
       "Max": 255,
       "Inclusive": true
     },
     "Unwrapped": false
   }
   

5. As a type with an operator:

   {
     "Type": "uint",
     "Operator": {
       "Type": "ge",
       "Value": {
         "Type": "literal",
         "Value": 0,
         "Unwrapped": false
       }
     }
   }
   

Type Combinations

Types can be combined in various ways:

1. As an array of alternative types (choices):

   "Type": [
     "tstr",
     "uint",
     {
       "Type": "literal",
       "Value": "default value",
       "Unwrapped": false
     }
   ]
   

2. As complex structures (groups and arrays):

   "Type": {
     "Type": "group",
     "Name": "address",
     "IsChoiceAddition": false,
     "Properties": [
       // properties...
     ],
     "Comments": []
   }
   

Usage in the AST

These basic types are used throughout the AST to define:

1. The type of a property in a group
2. The possible values of a variable assignment
3. The elements in an array
4. The parameters for operators

Understanding these basic types is essential for working with the AST and properly interpreting its structure.

Example

Here’s an example showing how different types are represented in a CDDL file and its corresponding AST:

person = {
  name: tstr,
  age: uint,
  is-active: bool,
  tags: [* tstr],
  status: "active" / "inactive" / "suspended"
}

The AST representation for this would include the various types we’ve discussed:

{
  "Type": "group",
  "Name": "person",
  "IsChoiceAddition": false,
  "Properties": [
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "name",
      "Type": ["tstr"],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "age",
      "Type": ["uint"],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "is-active",
      "Type": ["bool"],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "tags",
      "Type": [{
        "Type": "array",
        "Values": [{
          "HasCut": false,
          "Occurrence": { "n": 0, "m": Infinity },
          "Name": "",
          "Type": ["tstr"],
          "Comments": []
        }]
      }],
      "Comments": []
    },
    {
      "HasCut": true,
      "Occurrence": { "n": 1, "m": 1 },
      "Name": "status",
      "Type": [
        {
          "Type": "literal",
          "Value": "active",
          "Unwrapped": false
        },
        {
          "Type": "literal",
          "Value": "inactive",
          "Unwrapped": false
        },
        {
          "Type": "literal",
          "Value": "suspended",
          "Unwrapped": false
        }
      ],
      "Comments": []
    }
  ],
  "Comments": []
}

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