#cli #compiler #file-format #serialization #language #extra #languages #file


The verilization serialization description language compiler. This contains the CLI without any languages to allow adding extra languages.

1 unstable release

0.1.0 May 5, 2021

#749 in Development tools

22 downloads per month
Used in verilization-compiler-cli


2.5K SLoC


Verilization is a serilization description language designed for defining binary file formats. Unlike other serialization tools such as Protocol Buffers, serialized Verilization data is not forward or backward compatible. Instead, conversions from older format versions are made easy, allowing for more compact data and more control over the underlying shape of the data.


Verilization has the following primary goals.

  • Give maximum control of the file format to the user
  • Define the format in a language-independent manner
  • Support easy conversions from older versions of the format

Other less high-level goals.

  • Support bigint types
  • Embedable in other languages without using native binaries


The following types are supported.

Type Encoding
struct types The encoding of each field in order
enum types A tag (encoded in the same format as nat) followed by the encoding of the field represented by the tag
extern types Defined by code written in the target language


A struct type is defined with multiple versions. Each version defines a list of fields.

struct Rectangle {
    version 1 {
        width: u32;
        height: u32;


An enum type is defined with multiple versions. Each version defines a list of fields used as cases. An enum value consists of exactly one of these fields.

struct StringOrInt {
    version 1 {
        str: string;
        num: int;


An extern type is defined in user code. The type definition, conversions, and codecs must be implemented in the target language.

An extern type may declare what literals may be used for the type.

extern MyString {
    literal {

The following literal specifications are supported.

Name Example Syntax Notes
Integer integer [0, 256) 'integer' open_bracket integer_literal? ',' integer_literal? close_bracket
where `open_bracket : '['
'('andclose_bracket : ']'
String string 'string' The contents of the string cannot be restricted.
Sequence sequence T 'sequence' type_expr Defines a sequence of the specified type.
Case case Positive() 'case' identifier '(' [ type_expr { ',' type_expr } ] ')' Defines a case. Multiple case literals may be specified if the names are distinct.
Record record { a: A; b: B; } 'record' '{' { identifier ':' type_expr ';' } '}' Defines a record.

Runtime Library Types

There are a number of extern types provided by the runtime library.

Type Literals Encoding
{i,u}{8,16,32,64} Integers within the range of the type Fixed-width sequence of bytes in little endian order
int Integers A variable-length format
nat Non-negative integers Similar format to int, but without the sign bit
string Strings A length nat followed by a sequence of UTF-8 bytes with the specified length
list T sequence of T A length nat followed by a sequence of T
option T Two cases some(x) and none() A byte b. If b is non-zero, then it is followed by a T

The encodings for int and nat define a sequence of bits in little-endian order. The highest bit in each byte is set if there are more bytes in the number.

This encoding is a sequence of bytes [B0, ..., Bn] where Bi,7 = 1 when i < n and Bn,7 = 0. This sequence of bytes is equivalent to a sequence of bits [B0,0, ... B0,6, ..., Bn-1,0, ..., Bn-1,6] = [b0, ..., bm-1] where m = 6n. Essentially, the sequence of bits removes the flag bits that are used to determine when the sequence has reached the end and orders the remaining bits in each byte from least to most significant. The sequence of bits is mapped as follows:

  • For the int type, if bm-1 = 0, then k = b0 * 20 + ... + bm - 2 * 2m-2
  • For the int type, if bm-1 = 1, then k = -(b0 * 20 + ... + bm - 2 * 2m-2) - 1
  • For the nat type, k = b0 * 20 + ... + bm - 1 * 2m-1


In the following example, a user has a username and birth date.

struct Person {
    version 1 {
        name: Name;
        dob: Date;

struct Name {
    version 1 {
        firstName: string;
        middleName: option string;
        lastName: string;

However, not everyone has 2 or 3 names. In order to accomodate this, we can create a new version that allows for an arbitrary number of names.

struct Name {
    version 1 {
    version 2 {
        names: list string;

This change to Name means that in version 2 of the format, the name field of Person will now use version 2 of Name. However, since there are no direct changes to Person, version 2 is automaticly created. In the generated code, the user is expected to provide code that can upgrade Name from version 1 to version 2. However, there is no need to provide such code for upgrading Person. Person can be upgraded automaticially using the upgrade code for its fields.


Versioned types can be declared as final to indicate that no new versions of the type will be added. This restricts the type to the last explicitly declared version, preventing newer versions from being automaticially generated. Final types may only include fields of final or non-versioned types.

final struct FormatVersion {
    version 1 {
        major: nat;


Generic types allow a type to be parameterized.

final struct Pair(A, B) {
    version 1 {
        left: A;
        right: B;


Constants allow for values to be defined that are shared between any generated languages.

Literal Example Usage
Integer 88 extern types with integer literal
String "Hello World" extern types with string literal
Sequence [ a, b, c ] extern types with sequence literal
Record { x = 1; y = 2; } struct types and extern types with record literal
Case Name(a) enum types and extern types with case Name literal

Command Line

Verilization has a command line interface. The following options are supported.

Language Generators

The following languages are supported.

Compiler Bindings

The verilization compiler is written in Rust. It can be compiled into WebAssembly for use in other languages. This has the advantage that a tool can be distributed (for example, as an NPM package, a standalone JAR, etc) without requiring any native binaries. These bindings expose both an interface that can be used directly from the runtime, as well as a command line interface that depends only on the associated runtime.

Currently, there are bindings for the following runtimes.

  • Node


~49K SLoC