A Tydi language #116
Comments
|
Here is my brainstorm about this: // This is a brainstorm, not just a grammar definition or just examples,
// It's going to be a weird mix of both and more.
// I wrote this mainly from a user perspective, not from a compiler
// designer/implementer perspective.
// --------
// Literals
// --------
// signed integers, defaults to type i32
10 // decimal
1_0 // decimal
-10 // decimal
0xA // hex
0o12 // octal
0xb1010 // binary
// unsigned integers, defaults to type u32
10u // decimal
1_0u // decimal
-10u // ERROR
0xAu // hex
0o12u // octal
0xb1010u // binary
// character literals (ASCII or UTF8 ?)
'd'
'\n'
// string literals (ASCII or UTF8 ?)
"dolphins"
// half precision IEEE 754 floating point
1.0f16
// single precision IEEE 754 floating point
1.0f32
// double precision IEEE 754 floating point (the default)
1.
1.0
1.0f64
// quadruple precision IEEE 754 floating point
1.337f128
// octuple precision IEEE 754 floating point
42.0f256
// --------------------
// Builtin scalar types
// --------------------
// Null type - useful for e.g. user part of streams or generics (see e.g. Map
// below)
null
// Boolean types
bool // true or false
// Bit type
bit
// Should this hold VHDL-like std_logic values such as
// 0, 1, U, X, Z, W, L, H, - ?
// or probably better, like Verilog:
// 0, 1, X, Z
// -----------------------
// Builtin composite types
// -----------------------
// Integer types.
// Integer types consist of N bit parts that can be indexed or sliced (see
// below). Their numeric value is their two's complement value.
// Signed
int<N>
// Unsigned
uint<N>
// They have a size generic N, useful for type or generic propagation. N can be
// an expression, but it must resolve to a positive integer.
uint<0> // error
// These could maybe be aliased in a std lib as such?:
// Unsigned
u1, u2, u3, ... u(2^??)
// Signed
i1, i2, u3, ... i(2^??)
// Does a Rust-like u/isize make sense? Probably not, because there is no
// architecture. We *could* have isynth and usynth to refer to the compiler host
// architecture native integer size, but I currently lean towards not having
// something that could lead to portability issues.
// Floating-point numbers follow IEEE 754.
// While floats could be defined as structs (see below), we need them in generic
// arithmetic, so I think it's useful to define them as basic types.
// Operations on floats may not be synthesizable for now.
// Floating-point parts consist of their respective IEEE 754 fields, that can
// be indexed (but I don't think slicing makes sense here).
// IEEE 754 basic types:
f32, f64, f128 // binary floating point types
d64, d128 // decimal floating point types
// IEEE 754 non basic types:
f16, f256
d32
// Textual
char // ascii or utf8? or have byte for ascii and char for utf8 like Rust?
// I suppose "char" could make people uncomfortable w.r.t. encoding, so we could
// also have:
byte // obviously represented as 8 bits when used as net/port
ascii // represented as 7 bits (or do we want extended ascii?)
utf8 // represented as 32 bits
string // should we allow dynamic sizing? if so, it is not (easily)
// synthesizable. This type is meant for non-synthesizable stuff such
// as debug prints and generics.
// Maybe later:
// custom precision floating point ?
// fixed point ?
// posits ?
// Fixed-size array of size S elements of type T.
// S must be an expression of literals or constants
T[S]
// Tuples
// Should they carry the same semantics as struct (i.e. Tydi Group) ?
(T0, T1, ...)
// Product type
// Direction token for field (and port declarations, later).
> // (forward or out)
< // (reverse or in)
// Yes, these symbols are up for massive debates. And yes, I have already
// confused myself profoundly with it when typing port directions.
// Field declaration syntax:
// <attributes> <field identifier> <direction token> <type>
// Product type decl.
// Syntax:
// struct <identifier> {
// <field decl> (, <field decl>)*
// }
// Product type example:
struct LegacyStream {
valid > u1,
ready < u1,
data > u8
}
// Sum type decl
// Syntax:
// union <identifier> {
// <field decl> (, <field decl>)*
// }
// Sum type example:
// To define a net/port of type struct A outside of a stream,
// all values must be defined. Therefore, when A is used as a stream data type,
// for each handshake on X, there must be a handshake on Y. This is inherit to
// the Tydi spec representation of this stream as a stream of group<x, y>
union OptionalValue {
None > null,
Value > f64
}
// Variant decl:
// Syntax: <variant identifier> (= <custom value expression>)
// Enum type.
//
// Syntax:
// enum <identifier> (: <T>) {
// <variant decl> (, <variant decl>)*
// ...
// }
// Where T is the synthesized type. Perhaps analogous to "storage" type, this
// could be called "spatial" type. T will be log2ceil(num variants) number of
// bits when synthesized, unless explicitly defined to be otherwise.
// Enum type example:
enum ProtocolVersion {
IPv4,
IPv6
}
// Enum type with explicit spatial type and value
enum ProtocolVersion : u8 {
IPv4 = 0,
IPv6 = 0x1
}
// Tydi stream.
// A Tydi stream has three generics:
// T = the stream data type
// D = dimensionality, an expression or another generic from which a positive
// integer can be derived, default = 0
// U = user data type, default = null
// It may appear some of the original Tydi attributes for streams are missing.
// They are described elsewhere:
// - Direction is not defined here; it is declared through the struct or union
// field decl. This makes more sense, as direction is relative (to another
// field).
// - Synchronicity, same story, as the struct/union decl is the context in
// which child/parent relations are visible.
// - Complexity and throughput should be an attribute of a net or port,
// since they talk about properties of an interface but not of a data
// structure. Types should only capture unique properties of the data
// structure they represent.
stream<T, D, U>
// Stream examples:
stream<u8> // an infinite stream of u8s
stream<u8, 1> // an infinite stream of variable length sequences of u8s
// A stream of a struct type:
struct A {
x > u8,
y < u8,
}
// a stream with A.x in forward direction, A.y in reverse direction.
// To define a net of type struct A outside of a stream, all values must be
// defined. Therefore, when A is used as a stream data type, for each handshake
// on X, there must be a handshake on Y. This is inherit to the Tydi spec
// representation of this stream as a stream of group<x, y>
stream<A>
// A struct type with the synchronicity attribute set explicitly to flatten.
// This attribute is meaningless for non-stream nets or ports using this
// type (i think?)
struct B {
x > u8,
#[flatten]
y > u8 // if B were to be used in a stream with dimensionality > 0,
// only one y has to be transferred for each outermost
// sequence of x's.
}
stream<B, 1> // a stream with B.x with a last signal, and a stream with B.y
// without a last signal.
// A struct type with the synchronicity attribute set explicitly to desync.
struct C {
x > u8,
#[desync]
y > u8,
}
stream<C, 1> // Two streams with their own last signal. The same amount of
// sequences must be transfered, but each corresponding sequence
// can be of different length.
// I'm following the Rust attribute macro style here, but perhaps a nicer syntax
// is possible.
// ---------------------------------
// Builtin type operations/functions
// ---------------------------------
// It would be nice to have builtin special operators/functions so we can get
// properties of (stream) types, e.g. to be used in generic arithmetic.
DimOf(stream<T, 1>) // yields 1
// -------------
// Special types
// -------------
// We need to think about clocks.
// When using streams types, they always must have some associated clock.
// I would propose there is always an implicit global default clock domain with
// an associated clock and reset that will be propagated to any component using
// a stream type in their port list and does not explicitly define some other
// clock/reset to be used. I think this is also done in Spatial.
// It should be possible to define more clock domains to automate e.g. CDC.
clk // explicit clock type?
rst // explicit reset type?
// Random thought: associating stuff that uses clock/reset with it could look
// syntactically similar to Rust's lifetime specifier
// ------------
// Type aliases
// ------------
type CharStream = stream<char>; // This is a stream of char type without a
// last bit.
type String = stream<char, 1>; // A stream of char type with a last bit.
// -----------
// Expressions
// -----------
// We need expressions.
// At this stage, they will mainly be used to do arithmetic with generics and
// constants.
// Any decision here will have great impact on the language design, and needs
// some more thought. I personally like languages that are "expression
// languages" like Rust or Scala. (see:
// https://doc.rust-lang.org/reference/statements-and-expressions.html)
// At this point I don't feel qualified enough to come up with something good
// enough to discuss here so I will leave this completely open for suggestions.
// ---------
// Operators
// ---------
// Expressions require operators such as:
//
// + arith addition
// - arith subtraction
// * arith multiplication
// / arith division
// . member access?
// etc... needs more thought at this point, as described above.
// ---------
// Constants
// ---------
// syntax: const <identifier> : <type> = <expression>
// boolean types
const a = true;
const a : bool = true;
// numeric types
const a : u3 = 7; // u3
const a = 10; // i32
const a : u4 = -10; // error
const a = 10u10; // u10
// composite types
const a = [1, 3, 3, 7]; // array<4, i32>
const a = (42.0, 1.337); // tuple<2, f64>
const a = LegacyStream { valid = 0, data = 0 }; // LegacyStream
const a = OptionalValue::Value { 0.1 }; // OptionalValue
const a = ProtocolVersion::IPv4; // ProtocolVersion
// expressions can be used to define values, as long as the expressions use
// other constants.
const a = 0;
const b = 1;
const c = a + b;
reg a = 0;
const b = 1;
const c = a + b; // error
// -----
// Ports
// -----
// Syntax: <identifier>
// <direction token> <type>
// ('=' <default value expression>)
// ----------
// Components
// ----------
// Components are entities that help to build hierarchy and reusable parts of
// the design.
// While it is an awesome term, I don't think streamlet should be a keyword,
// since a streamlist is just a special case of a component for which all ports
// have a stream type, but they carry no special semantics that cannot be
// expressed with the component keyword.
//
// Syntax:
// comp <identifier>
// ('<' <generic list> '>')
// (':' <interface list>)
// ('(' <port decls> ')')
// ('{' <implementation '}')
//
// When a component has no defined implementation and is not marked "extern",
// (see below), the compiler should issue a black-box error by default, and not
// a warning that is buried under thousands of other useless warnings like we
// are used to from traditional HDLs / toolchains.
//
// A component should probably be a type itself?
// An adder
comp Add (
a < u8,
b < u8,
y > u8
) {
// implementation goes here.
// Referring to ports could be done through a keyword such as e.g. self:
self.y = self.a + self.b;
y // invalid reference
// Or could we omit self and not allow local declarations of stuff with
// the port name? This would result in smaller code, but it will have less
// local reasoning. I would personally still go for the latter.
y = a + b;
}
// An N-bit adder
comp Add<N: u64> (
a < u<N>,
b < u<N>,
y > u<N>
) {
// implementation goes here.
}
// -------------------
// Component instances
// -------------------
comp PlusOne<N: u64> (
a < u<N>,
y > u<N>
) {
// An instantiation of Add<8> with the identifier adder:
inst adder : Add<N>;
// VHDL-like associativity lists suck.
// We can refer to instance ports anywhere in implementation code as
// follows:
adder.a = a;
adder.b : u<N> = 1;
y = adder.y;
}
// --------------------
// Component attributes
// --------------------
// It may be useful for later on if we could give components specific
// attributes, such as:
#[streamlet]
comp foo (
// only ports with the stream type are allowed.
);
// Perhaps to even define latency useful for building larger designs with
// automated buffering, if it cannot be derived automatically of course.
#[streamlet, latency={{a,b,5},{a,c,6}}]
comp foo (
a < stream<...>,
b > stream<...>,
c > stream<...>,
);
// -------------------
// External components
// -------------------
// (Imperfect analogies ahead:)
// Using the "extern" keyword and an "RTL" specifier, it is possible to declare
// a component is implemented outside this hardware description. We need to
// think about how far we could take this. There is no real "ABI" for hardware
// so we must think about how the build tool "links" such an external component
// into the target output. Hence I called it "RTL" here but perhaps there is a
// better name for this. It would be possible to "link" such components into the
// design when they use e.g. the Tydi canonical representation of it in VHDL,
// SystemVerilog, Verilog, or lower level stuff like FIRRTL. For the traditional
// HDLs mentioned here, the build tool must know how to deal with such external
// sources.
// Example:
extern "VHDL" comp foo (
i < u8,
o > u8
); // implementation is omitted.
// ----------------------------------------------
// Special attributes for ports with stream types
// ----------------------------------------------
comp X (
#[throughput=10, complexity=5]
a < stream(u8)
);
// ----
// Nets
// ----
// Nets are simply wires between things within a component implementation, like
// the Verilog "wire" keyword. They do not have the semantics of VHDL "signal"s
// as in that they could be used to create registers.
//
// Syntax:
// net <identifier> (: <type>) (= <expression>)
net q : u8 = 1; // a net named q of type u8 tied to 0b00000001
net r = q; // a net named r of type u8 driven by q.
net s = stream<u8>; // a net named s of type stream<u8>. If nothing drives this
// net, the default value of the streams "valid" is
// de-asserted with the other values don't care.
net t : stream<u4> = s; // Error.
// ----------------
// Registers (TODO)
// ----------------
reg x = 0;
// -----------
// Connections
// -----------
// Connections declarations of source and sink connections.
// Syntax:
// <destination identifer> = <expression>;
// Source can be any expression. Perhaps the assignment symbol = should be an
// operator, and the assignment should be an expression itself that yields a
// reference to the net being driven, so you can chain like: a = b = c;.
// Example:
comp X (
a < u8,
b > u8
) {
b = 0; // drives b to zero (all bits are typically ground).
a = 0; // error, a is an input.
b = a; // drives b with a.
a = b; // error, a is an input.
}
// --------------------------------------
// Selecting and slicing into basic types
// --------------------------------------
// Single part/element selection and slicing is done through the [] operator.
// Range expression:
// Syntax: <inclusive start index> .. <exclusive end index>
// Syntax: <inclusive start index> ..= <include end index>
// etc.., see Rust.
// Slicing into arrays:
net a : array<u8, 3> = [1, 2, 3];
net b : array<u8, 2> = a[0..1];
net c : array<u8, 2> = a[1..];
net d : array<u8, 2> = a[..1];
net e : array<u8, 2> = a[0..3]; // error
// Slicing into numeric types is allowed for numbers that have "parts"
// (somewhat following Verilog terminology here), i.e. int<N>, uint<N> and f32,
// f64, f128, d64, d128.
// Slicing into integer parts
net a : u8 = 1;
net b : bit = a[0];
net c : a[0..3]; // becomes a u4
net d : a[4..8];
// Selecting float parts:
net e = 0.1; // f64
net f = e.sign; // bit
net g = e.exp; // i don't even want to go into this.
// Selecting stream parts:
net h = stream<u8>;
net i : bit = h.valid;
// --------------------------------------------
// Generative structural expressions/statements
// --------------------------------------------
// Conditional generate
// Syntax: gen if <bool expression> { <statements> } else { <statement> }
// Example:
gen if a = 0 {
b = c;
} else {
b = d;
}
// Pattern matching generate
// Syntax: gen match <expr> {
// <expr> : { <statements>},
// ...,
// }
// Example:
gen match a {
0 : { b = c; }
1 : { b = d; }
_ : { b = 0; }
}
// Generative for
// Syntax: gen for <iterator> in <iterable> { <statements> }
gen for I in [1, 2, 3] {
inst a;
}
// How could we refer to some instance of a?
// What if we could have arrays of instances?
// ----------
// Interfaces
// ----------
// Interfaces are pre-defined sets of port declarations with associated
// generics, that may be implemented by components. They are useful when
// when components have generics that take other components as an argument, to
// scope the allowed components according to some interface specification.
// Syntax:
// interface <identifier>
// ('<'<generic list>'>')
// '(' <port decls> ')'
// Example for a Map interface:
interface Map<type I, type O, type U=null> (
input < I, // input port
output > O, // output port
user < U // custom data port
);
// Example of a component implementing the Map<u8, u8, u8> interface.
// This component will increment elements of i by u.
comp Incrementer : Map<u8, u8, u8> {
// impl goes here
}
// Could be equivalent to:
comp Incrementer : Map (
// I and O could be inferred using this syntax:
Map::input < u8,
Map::output > u8,
Map::user < u8
) {
// impl goes here.
}
// Example continued:
// A component with a component generic requiring the above Map interface.
// This component would implement a one-to-one mapping of every element of the
// sequence of i to o. U is used for a custom net to the MapComp that can be
// used for e.g. run-time parameters, but is null by default.
comp MapSeq<type I, type O, comp C : Map<I, O, U>, type U=null> (
input < stream<I, 1>, // Input sequence.
// I'm assuming here if I = stream<T, 1>,
// stream<I, 1> becomes stream<T, 2>.
output > stream<O, 1>, // Output sequence.
user < U // Custom signals to the internal instance of C.
) {
inst map : C;
map.user = user;
// More implementation would follow here, but requires non-structural stuff.
}
// Example continued:
comp Top (
i < stream<u8, 1>,
o > stream<u8, 1>
) {
inst inc_seq : MapSeq<u8, u8, Incrementer, u8>;
// Increment every element by 42.
inc_seq.u : u8 = 42;
inc_seq.i = i;
o = inc_seq.o;
}
// Example of a reduce component.
// Reduces two values to one, given some initial value.
interface Reduce<type T, type U=null> (
input_0 < T,
input_1 < T,
output > T,
user < U
)
// Example continued:
comp Add<T> : Reduce<T> {
// This would implement: output = input_0 + input_1;
}
// Example continued:
// Reduces a sequence
comp ReduceSeq<type T, comp C : Reduce<T, U>, type U=null> (
initial < stream<T>, // initial value
input < stream<T,1>, // input sequence
output > stream<T>, // reduced result
user < U // custom signals to the internal instance of C.
) {
inst reduce_seq : C;
reducer.user = user;
// More implementation would follow here, but requires non-structural stuff.
}
// Example continued:
comp Top (
numbers < stream<u8, 1>,
sum > stream<u8>
) {
inst reducer : ReduceSeq<u8, Add<u8>>;
reducer.i = numbers;
reducer.d = 0;
sum = reducer.o;
}
// Components can implement multiple interfaces:
interface X ( a > u8 );
interface Y ( a < u8 );
comp Z : X, Y {
// impl goes here
X::a // refers to port a of interface X
Y::a // refers to port a of interface Y
a // error, undefined.
}
// --------
// Packages
// --------
// Packages are namespaced collections of types, constants and components.
// The package name "work" is reserved for the root namespace.
// Example:
package X {
type String = stream<char, 1>;
const pi = 3.14;
comp foo {
a < u8,
b > u8
}
}
// Packages and their constituents can be used without their nasmespace
// through a use declaration.
// Example:
use X::*; // use everything
use X::{String, pi}; // use only specific stuff
comp bar {
inst moo : X::foo;
}
// The root namespace for a project is "work".
inst a : work::bar;
inst b : work::X::foo;
// ------------
// Doc comments
// ------------
// Doc comments start with three slashes: /// and are placed in front of the
// declaration to be documented.
// Example:
/// A dolphin
struct Dolphin {
/// The name of the dolphin.
name : String,
/// The size of the dolphin in cm.
size : u32
}
/// An interface for components producing Dolphins.
interface DolphinProducer (
/// Dolphin output.
o > Dolphin,
)
// ----------------------
// An example from TPCH-6
// ----------------------
// SELECT
// sum(l_extendedprice * l_discount) as revenue
// FROM
// lineitem
// WHERE
// l_shipdate >= date '1994-01-01'
// AND l_shipdate < date '1995-01-01'
// AND l_discount between 0.06 - 0.01 AND 0.06 + 0.01
// AND l_quantity < 24;
/// Package with components performing TPC-H queries.
package tpch {
/// A date.
struct Date {
year > u12,
month > u4,
day > u5,
}
/// A range (dynamic).
struct Range<T> {
/// Start value (inclusive)
start > T,
/// End value (exclusive)
end > T,
}
/// A row from the LineItem table.
struct LineItem {
extended_price > f64,
discount > f64,
ship_date > Date,
quantity > f64,
}
/// Parameters for TPC-H query 6
struct Q6Params {
/// The shipdate range for which the revenue must be calculated.
shipdate_range < Range<Date>,
/// The discount range for which the revenue must be calculated.
discount_range < Range<f64>,
}
/// Interface for filter predicates
interface Predicate<T> {
i < T,
o > bool,
}
/// Component implementing the Predicate interface, outputting true for T's
/// that fall within the range, false otherwise.
comp WithinRange<T> : Predicate<T> (
range < Range<T>,
) {
// impl goes here.
}
/// TPC-H Query 6 with dynamic shipdate and discount ranges.
comp Q6 (
/// Parameters for the query on each table.
params < stream<Q6Params>,
/// The stream of tables to operate on.
tables < stream<LineItem, 1>,
revenue > stream<f64>,
) {
/// The ship date filter. See definition of MapSeq above.
inst date_flt : MapSeq<Date, bool, WithinRange<Date>, Range<Date>>;
/// The discount filter.
inst discount_flt : MapSeq<f64, bool, WithinRange<f64>, Range<f64>>;
// The params stream has members that go different ways. It's probably
// good to make the sync explicit. Perhaps it could look like this:
date_flt.range, discount_flt.range = params.split({shipdate_range},
{discount_range});
// With .split(...) which should be a builtin member of a stream type,
// you can split the streams out (at your own risk) to any combination.
// Each argument of split is a list of members that should stay
// together. This results in new (anonymous) types.
// Implicit stream split could be a thing:
date_flt.range = params.shipdate_range;
discount_flt.range = params.discount_range;
// Warning! Control flow ahead - non-goal for now so can be safely ignored.
// Just a brainstorm.
// For each table (this continues indefinitely unless reset is asserted).
for table in tables {
// For each row in the table.
// This continues up to when the tables last bit is asserted.
date_flt.input = row.shipdate;
discount_flt.input = row.discount;
// TODO
}
// end of control flow
}
// ---------------
// Random thoughts
// ---------------
// It would be nice if generics are Turing-complete.
// It would be nice if generics could interface with the file system.
// --------------------------------------------
// Random examples that got lost in the process
// --------------------------------------------
struct Dolphin {
name : String, // This is a stream
size : u32, // This is not a stream
}
/// This component feeds baby dolphins until they are the size of a grownup
/// model and then outputs them.
comp Feeder {
// Since Dolphin.size is not a stream for model, there is no
// synthesized synchronization between model.size and model.name.
// Users are on their own in terms of how to synchronize between the fields
// of the struct.
model < Dolphin,
// However, in the following case, a stream is wrapper around it.
// We will interpret this as a Stream<Group< .... >> in the spec,
// so for each name of the inner stream for name, also one size must be
// handshaked on the outer stream for size.
baby < stream<Dolphin>,
grownup > stream<Dolphin>,
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
This is a tracking issue for the first steps towards implementing a hardware description language for Tydi types.
Currently the Tydi crate provides modules with the logical and physical stream type definitions and methods as described in the specification. There is also a design module that defines streamlets, a parser module for streamlet definition files and a generator module that can generate HDL templates based on streamlet definition files. The
tydicommand line application exposes these capabilities.In order to provide an ergonomic solution for #51, this issue tracks the requires steps to move from an (embedded) library based approach to a high-level language approach. This issue attempts to provide tasks and steps for the initial phase of the language, compiler and tooling design.
Motivation
The benefits from adapting Tydi typed streams (🐬) in hardware designs may be snowed under the added effort and struggle (🐠) for hardware developers to make their designs compatible with Tydi streams.
Goals
The goals during this phase
for the Tydi language:
for the tooling:
Non-goals
During this phase the Tydi language does not support:
Design
Syntax
Tydi's syntax is heavily inspired by Rust's syntax.
Tokens
.td.Keywords
Punctuation
Literals
Grammar
Documented example of Tydi source file using the proposed grammar:
The grammar listed here is a proposal and open for discussion. There are already several issues to be discussed:
LL(1)parsingconst N: i32Semantics
const N: ??Compiler
The Tydi compiler takes Tydi source files, parses them into an abstract syntax tree, resolves names, checks types and generates an in-memory high-level intermediate representation (hir) that can be used by backends for compiler output. References to sources are tracked outside the hir to allow us to provide a library for construction of these structures for generation tools (similair to the current approach).
In the initial phase of the project (type and streamlet definitions only) the compiler output consists of purely structural HDL templates (and helper methods) or design visualizations.
Project
A Tydi project consists of a manifest (
tydi.toml) with project meta information and source files with type and streamlet defintitions.Manifest
tydi.tomlis a project's manifest file that contains all metadata and configuration information about the project.The Tydi manifest file is inspired by Rust's Cargo.toml.
Example
This example
tydi.tomlshows all valid fields of a project manifest.Structure
The files in a Tydi project are organised with the project manifest in the root directory of the project, and all module files in a
srcdirectory. Thetargetdirectory is used for compiler output. This setup is inspired by Rust'scargobehavior.Example std.td
Tasks
log2!tydicliFuture work
impl Adder { ... }type Foo = Bit; type Bar = Bit;->Foo as BarThe text was updated successfully, but these errors were encountered: