hopp/design/pdl.md

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
I1281	LI	15
I2561	LI	31
U5	SI
U8	LI	0
U16	LI	1
U32	LI	3
U64	LI	7
U1281	LI	15
U2561	LI	31
F16	FP	1
F32	FP	3
F64	FP	7
F1281	FP	15
F2561	FP	31
String	SBA/LBA	*	UTF-8 string
Buffer	SBA/LBA	*	Byte array
[]	OTA	*	Array of any type2
Table	KTV	*

Tokens

Name	Syntax
Method	M[0-9A-Fa-f]{4}
Key	[0-9A-Fa-f]{4}
Ident	[A-Za-z][A-Za-z0-9]
Comma	,
LBrace	{
RBrace	}
LBracket	[
RBracket	]

Syntax

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:

M0000 Connect {
	0000 Name String,
	0001 Password String,
}

M0001 UserList {
	0000 Users []User,
}

User {
	0000 Name      String,
	0001 Bio       String,
	0002 Followers U32,
}

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1. Some systems may lack support for this. ↩︎

2. 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. ↩︎