Z# (Zee-sharp)

A new .NET language

Identifiers

Identifiers name program entities such as variable, functions and types. These names must follow these rules:

Here are examples of valid identifiers:

My_Function1
someVariable
_hidden
prime'

Here are examples of invalid identifiers:

1Function
some variable
my-type

TBD: I don’t see any objection to add ‘-’ (minus sign) as a valid character for an identifier…? Or start an identifier with a digit? The parser should be able to match that correctly.

TBD: Is there a practical reason not to allow special characters or even names that only consist of special characters (as custom operators)?

TBD: Specifically allowing . in an identifier could provide some flexibility for applying namespaces within a module. It could also be used to separate name parts with a non-optional character (_ is an optional character).

Symbols and Labels

A general kind of identifiers are code labels.

This syntax is basically consistent of all named code elements.

symbol: <some other code>
#label: <some other code>

Symbols will be compiled into the binary while labels are only available at compile-time.

This allows some language features where an identifier/label/symbol refers to some specific code.

Label Code Type Description
var x: U8 Type Variable declaration
fn fn: (p: U8): U8 FunctionType Function declaration
struct MyStruct Type Structure declaration
field fld: U8 Type Field declaration
loop #outer: loop 42 LocationType Loop identifier*

*) The label is prefixed with a # to indicate it is a compile-time label and not a symbol that will be in the binary.

Case Sensitivity

Identifiers are the same when:

TBD: exclude function names from having to match case of first letter of function name? That would allow for fully adapting your own naming conventions - at least for functions. Types still have to start with a capital first char.

Discard

Using a discard _ in an identifier is ignored during matching.

My_Function: (p: U8)
    ...

Myfunction(42)  // calls My_Function

//----

Myfunction: (p: U8)
    ...

My_Function(42)  // calls Myfunction

When an identifier only consists of a discard _ it indicates it is not used.

myFn: (_: U8): U8    // param not used
    ...
_ = myFn(42)        // return value not used

If an identifier starts with a _ it is hidden from immediate public access. The field will be internal in .NET for an exported structure, otherwise it’ll be private.

MyStruct
    _id: U32
    Name: Str

s: MyStruct
s.[intellisense does not show _id]

Do we want to give meaning to identifiers ending with a _? Could we use this for weak-functions (or weak-anything)?

TBD: We could also use _ as a prefix for any symbol to indicate it is a private symbol. This would not require to explicitly export a public symbol.

_privateFn: ()
    ...
publicFn: ()
    ...

Fully Qualified Names

MyModule.v2.MyFunction

Do we want to distinguish between namespace separators and obj.fn() calls?

// namespace / module name (also for import, export aliases)
MyModule::v2::MyFunction

// function call
obj.MyFunction(42)

Only needed when function call may include namespace/module parts…

Any identifier that has a . (dot) in it will be split up in parts. Those parts will be used to navigate to the correct ‘location’ where that symbol is defined.

For now, relative navigation is only supported for symbols that do not have dot-name. In the import statement, long navigation paths (namespaces) can be aliased to shorter names to be used in the module’s source code.

import statements for external modules are always specified in absolute (fully qualified) names. import statements for local modules are specified with relative (in the same namespace) or absolute names.

// external module
import System.Console   // type
import System.*         // namespace

// local module
import myModule         // module (type)
import namespace.module // same as external module

Fully qualified names in code are resolved during compilation.

// this should not require an import statement
fn: ()
    System.Console.WriteLine("Hello World")

Navigation into fields does work relatively.

MyStruct
    fld1: U8
    fld2: Str

s : MyStruct =
    fld1 = 42
    fld2 = "42"

// struct field navigation
x := s.fld1

MyEnum
    Opt1
    Opt2

// enum field navigation
e := MyEnum.Opt1

Prefixes

Identifier prefixes are special ‘keywords’ that signify a special meaning to the construct identified.

Identifier prefixes are only used at the definition not for the reference.

To interop with .NET properties the get_ and set_ prefixes are used to target property setters and getters.

// static property
get_MyProp: (): U8
    return 42

// instance property
get_MyProp: (self: MyStruct): U8
    return self.field1

// call static property
p := MyProp      // no () required?
Prefix .NET Description
get_ property get Implements a property getter.
set_ property set Implements a property setter.
opchk_ - Z# operator checked implementation (exception).
opuchk_ - Z# operator unchecked implementation (wrap).
op_ - Z# operator implementation where return type indicates semantics (Err<T>/Opt<T>)
opsat_ - Z# operator implementation that saturates?

Perhaps start the prefix with a _ to indicate that part is hidden?

Aliases

Almost all identifiers can be aliased, given a new name that is resolved at compile time. These aliases themselves are identifiers and follow the same rules.

An Alias is created by assigning it an existing identifier.

Fn: (p: U8)
    ...

MyAlias = Fn

MyAlias(42) // calls Fn(42)

TBD

When an alias resolves to nothing (or empty string) it is treated as a weak reference and removed from the code.

This would allow conditional compilation to select different ‘implementations’ for an alias or even leave it empty when it does not apply.

// alias resolves to nothing
MyEmptyAlias = _

// entire call removed because alias is empty
MyEmptyAlias(42)