# PDL Language Definition PDL allows defining a protocol using HOPP and TAPE. ## Data Types | Syntax | TN | CN | Description | ---------- | ------- | -: | ----------- | I5 | SI | | | I8 | LI | 0 | | I16 | LI | 1 | | I32 | LI | 3 | | I64 | LI | 7 | | I128[^2] | LI | 15 | | I256[^2] | LI | 31 | | U5 | SI | | | U8 | LI | 0 | | U16 | LI | 1 | | U32 | LI | 3 | | U64 | LI | 7 | | U128[^2] | LI | 15 | | U256[^2] | LI | 31 | | F16 | FP | 1 | | F32 | FP | 3 | | F64 | FP | 7 | | F128[^2] | FP | 15 | | F256[^2] | FP | 31 | | String | SBA/LBA | * | UTF-8 string | Buffer | SBA/LBA | * | Byte array | []\ | OTA | * | Array of any type[^1] | Table | KTV | * | Table with undefined schema | {...} | KTV | * | Table with defined schema [^1]: Excluding SI and SBA. I5 and U5 cannot be used in an array, but String and Buffer are simply forced to use their "long" variant. [^2]: Some systems may lack support for this. ## Tokens PDL files are divided into tokens, which assemble together into larger language structures. They are separated by whitespace. | Name | Syntax | Description | -------- | ------------------ | ----------- | Magic | `PDL/0` | Must appear at the very start of the file. | Method | `M[0-9A-Fa-f]{4}` | A 16-bit hexadecimal method code. | Key | `[0-9A-Fa-f]{4}` | A 16-bit hexadecimal table key. | Ident | `[A-Z][A-Za-z0-9]` | An identifier. | Comma | `,` | A comma separator. | LBrace | `{` | A left curly brace. | RBrace | `}` | A right curly brace. | LBracket | `[` | A left square bracket. | RBracket | `]` | A right square bracket. ## Syntax All files must begin with a Magic token. Types are expressed with an Ident. A table can be used by either writing the name of the type (Table), or by defining a schema with curly braces. Arrays must be expressed using two matching square brackets before their element type. A table schema contains comma-separated fields in-between its braces. Each field has three parts: the key number (Key), the field name (Ident), and the field type. Tables, Arrays, etc. can be nested. Files directly contain messages and types, which start with a Method token and an Ident token respectively. A message consists of the method code (Method), the message name (Ident), and the message's root type. This is usually a table, but can be anything. Here is an example of all that: ``` PDL/0 M0000 Connect { 0000 Name String, 0001 Password String, } M0001 UserList { 0000 Users []User, } User { 0000 Name String, 0001 Bio String, 0002 Followers U32, } ``` ## EBNF Description Below is an EBNF description of the language. ``` -> ( | -> "PDL/0" -> /M[0-9A-Fa-f]{4}/ -> /[0-9A-Fa-f]{4}/ -> /[A-Z][A-Za-z0-9]/ -> -> | "[" "]" | "{" ( ",")* ? "}" -> -> ``` ## Go Code Generation Given one or more PDL files representing a protocol, the compiler shall generate a Go package named "protocol", which shall contain types for message and type definitions, as well as encoding and decoding methods. ### Static Section The compiler shall write a static section alongside the generated code. It shall contain this text: ```go // Table is a KTV table with an undefined schema. type Table map[uint16] any // Message is any message that can be sent along this protocol. type Message interface { codec.Encodable codec.Decodable // Method returns the method code of the message. Method() uint16 } ``` ### Preamble At the start of each file but after the package name, the compiler shall emit this text: ```go /* # Do not edit this package by hand! * * This file was automatically generated by the Holanet PDL compiler. The * source file is located at * Please edit that file instead, and re-compile it to this location. * * HOPP, TAPE, METADAPT, PDL/0 (c) 2025 holanet.xyz */ ``` Where `` is the path of the protocol definition file relative to the generated file. ### Message Definitions For each defined message, the compiler shall generate a Go type named `MessageName`, where `Name` is the name of the message as written in its definition. The message shall be encodable, and shall have `Encode` and `Decode` methods as described below. All messages shall satisfy a `Message` interface, which is defined in the static section. ### Type Definitions For each defined type, the compiler shall generate a Go type with the same name as written in its definition. The Go type shall be encodable, and shall have `Encode` and `Decode` methods as described below. ### Encoding and Decoding Methods Each encodable type shall be given an `Encode` method and a `Decode` method, which will take in a `codec.Encoder` and a `codec.Decoder` respectively. Both return an `(int, error)` pair describing the amount of bytes written and an error if the write stopped early. `Encode` will encode the data within the message to the given encoder, and `Decode` will decode data from the given decoder and place it in the type's value. The methods shall not retain or close any encoders or decoders they are given. Both methods shall have pointer receivers. In effect, these methods will satisfy `codec.Encodable` and `codec.Decodable`. ### Connection The compiler shall generate a `Conn` struct which embeds a `hopp.Conn`, which is the real "porcelain" of the generated code. Any