Operators

Most operators are syntactic sugar over a set of wellknown functions.

Of these wellknown functions there are two flavors: unchecked and checked implementations. The unchecked flavor performs no validation. The checked version implements extra validation and ‘checking’ to help make sure the code is correct.

Use identifier prefixes to identify checked/unchecked operator functions implementations. (checked_ / unchecked_?) Or use a namespace for interop? Checked.ArithmeticAdd() The namespace can either be a dotnet namespace or static (nested) class.

TBD

Add specific operators for arithmetic operations for saturation (ignoring overflow and filling up till full) and wrapping (wrapping around to start over again when full) behavior.

Postfix arithmetic operator with:

Operator	Description
\|	Overflow/underflow will saturate.
%	Overflow/underflow will wrap around. (.NET unchecked)
~	Overflow/Underflow will cause an exception. (.NET checked)
!	Overflow/Underflow will return an error (Err<T>).
?	Overflow/underflow will result in Nothing (Opt<T>).

a: U8 = 245
b: U8 = 125

c: U8 = a +| b  // saturate (255)
c: U8 = a +% b  // wrap around (115)
c: U8 = a +~ b  // overflow exception (370 > U8)
c: U8! = a +! b // Error (Err<U8>)
c: U8? = a +? b // Nothing (Opt<U8>)

// Is checked `~` the default? or use .NET default (unchecked?)
c: U8 = a + b   // ??

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Precedence

In order of precedence (top is highest):

Operator	Description
Unary	Unary operators are always applied first
Binary	infix operators typically require ()
Ternary	ternary operators are applied last.

That means that an expression with multiple (binary) expressions MUST use ( ) to indicate the order of execution - unless all the operators are the same.

We may need to define precedence between the different types of operators as well. So arithmetic operators should run before comparison operators for instance. It would probably look a bit silly if you had to put parenthises around a < x + y.

Operator	Description
Arithmetic, Bitwise	Use parenthises to determine order.
Comparison	Compare with ‘values’ complete (previous).
Logical	Combine mulitple boolean (comparison) expressions last.

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Operator Symbols

Arithmetic, comparison, bitwise and logical operators.

Operator	Fn Name	Description
+	ArithmeticAdd	Addition / Absolute? (unary)
-	ArithmeticSubtract, ArithmeticNegate	Subtraction / Negation (unary)
*	ArithmeticMultiply	Multiplication
/	ArithmeticDivide	Division
%	ArithmeticRemainder	Remainder
**	ArithmeticPower	Power (3 ** 2 = 9)
//	ArithmeticRoot	Root/Log (9 // 2 = 3)
%%	ArithmeticModulo	Modulo (negative numbers)
( )	-	Infix Operator Precedence, Function Call, List Literal, Tuple/deconstruct
=	IsEqual	Equals (value equality, is for identity?)
<>	IsNotEqual	Not Equals (value inequality, is not for identity?)
>	IsGreaterThan	Greater than
<	IsLesserThan	Smaller than
>=	IsGreaterEqual	Greater or Equal
=<	IsLesserEqual	Smaller or Equal
?	AsBoolean	Boolean postfix
? :	-	Ternary Conditional (if-else) (don’t like the : used for types everywhere else)
? ;	-	-alt- Ternary Conditional (if-else)
and	LogicAnd	Logical And
nand	LogicAnd	Logical Nand?
or	LogicOr	Logical Or
nor	LogicOr	Logical Nor?
xor	LogicXor	Logical Xor
nxor	LogicNxor	Logical Nxor?
not	LogicNot	Logical Negation
&	-	Bitwise And*
\|	-	Bitwise Or*
^	-	Bitwise Exclusive Or*
~	-	Bitwise Negation (complement/invert)*
>>	-	Bitwise Shift Right
<<	-	Bitwise Shift Left
>\|	-	Bitwise Rotate Right
\|<	-	Bitwise Rotate Left
->>	-	sign extend (arithmetic) bit shift right
>>>	-	-alt- sign extend (arithmetic) bit shift right
=	-	Value Assignment
:=	-	Value Assignment with inferred Type
<-	-	Value Assignment of mutable Type? (TBD)

TBD: *) we could reuse the logical operators for use as bitwise operators as well. That also means that the bitwise short-hand operators (&=, |= or ^=) no longer work.

Ternary operators can contain other ternary operators. Nested ternaries each have their own indent level.

x := a > b 
    ? a 
    : b > c
        ? b
        : c

No other formatting is supported for nested ternaries.

TBD: Can ternary be an l-value - that can be assigned to?

x := 0
y := 1

// result is (a ref to) the var not the value of the var.
(x > y) ? x : y = 42

Allow logical not to be prefixed to other logical operators? nand, nor, xnor or use dedicated keywords?

More mathematic concepts as operators? PI (and other constants), rad, deg, vectors, matrix, infinity, sin, cos, tan (inv), rounding (floor, ceiling), medium, mean, average, factorial/permutation/combination, sum…

Operator that cascades the left value? See C# pattern matching with is: if c is 42 or 101. So instead of if c = 42 or c = 101 you can write something like if c = 42 || 101. See also match expression. Would also work with if c in (42, 101).

Operator	Fn Name	Description
&&	cascading l-value logical-and
\|\|	cascading l-value logical-or

TBD: The is expression is probably easier to read and understand. No extra operators needed.

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Other Symbols

Symbol	Description
_	Unused / Discard / Hidden
.	Members Access / bound access
..	Range operator
...	Spread operator
,	List Separator (or use expression separator?)
:	(Sub)Type Specifier
;	Expression separator (like in F#)
< >	Type Parameter
( )	Function / Tuple / Array/List initialization
" "	String Literal
' '	Character Literal
'' ''	Special Name
@	Disable String formatting features / keyword escape?
{ }	String formatting parameter / Code Decorator / Object construction
[ ]	Index / Slice / Range / Capture
\| \|	Alternate Capture
!	Possible Error (return type)
?	Optional variable or parameter/return value / boolean operator / fallback
?=	Optional variable conditional assignment
->	Line continuation (instead of indent)
#	Pragma / Attribute access / Execute at compile-time
#!	Compile-time code definition (perhaps only #)
#!	Compile-time error (alt)
#?	Compile-time warning
##	Temporary comment (compiler warning)
#xxx:	Compile-time label ‘xxx’ used to identity code blocks / scopes
#_	Comment

In case of a fallback ? we could use or perhaps? opt? or 42 Use the ? as the boolean operator and or for chaining. opt1? or opt2? or 42

#! does make the distinction clear between compile-time functions and for instance inline exported functions: #export fun: ()... vs. #! fun: () ....

Are there others like conditional assignment ?=? Can any (applicable) operator be made conditional by prefixing ? to it?

Symbol	Description
?=	conditional assignment
?+	conditional add
?-arithmetic	conditional any arithmetic operation
?+=	conditional read-add-write

a: U8 = 42
o: U8? = _

// on which side is the optional?
x := a ?+ o
// does it matter?
x := o ?+ a

TBD: chaining bools with ? => No, use or.

tryFn(p: U8): Bool
    ...

b = tryFn(42) or tryFn(101)

// self-bound example
tryFn(self: Str, p: U8): Bool
    ...

s := "42"
// use auto-fluent syntax?
b := s.tryFn(42) or/and 
    .tryFn(101)

// pattern matching ??
b := s is tryFn(42) or tryFn(101)    // weird

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Type operators

Symbol	Type	Description
!	Err<T>	Error return value or T
?	Opt<T>	Optional; T or Nothing
*	Ptr<T>	Pointer to T
^	Mut<T>	Mutable T
%	Atom<T>	Atomic T
??	Async<T>	Async T ??

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Reserved Operator Symbols

All non-characters and numbers are reserved at this point.

To be determined:

Operator	Description
\	reserved
$	to string / auto-constant string checked by compiler.
!	reserved (factorial?)
?.	Safe Navigation
=>	used in mapping / some sort of (forward) assignment? (implies?)
<=	map structure / assign struct properties
()	Function Object operator
\|>	Parameter pipe
<\|	Reverse parameter pipe (don’t like it)
<=>	Swap operator
::	traits? (type of type)
<-	reserved (assign mutable variable?)
->>	parallel execution (also sign extended shift)
=>>	parallel execution and collect results (in tuple or deconstruct)
[[ ]]	Alternate Decorators syntax (instead of {})
[< >]	Type Decorators (Attributes) syntax (instead of {})
[( )]	Function Decorators syntax (instead of {})

Notes on safe navigation ?.:

In an expression that chains several safe navigations together in a path, the result may become a little hard to read.

x := root?.obj1?.obj2?.prop1

Perhaps we could come up with something that turns on safe navigation for the entire expression?

x := ?root.obj1.obj2.prop1

Is there use for safe navigation in collections?

// safe indexing?
x := root.collection[?0]    // x: Opt<T>

Use of safe navigation (in any form) always results in an Optional Opt<T> that is nothing if the path could not be navigated completely.

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Type Operator Symbols

Operators that operate on types.

Operator	Description
:=	equals type (bool/condition) (also assignment with type inference)
:?	type is (C# is keyword)
<:?	type as (optional cast)
<:	down cast type
:>	up cast type? (is implicit)

Alternatives where the : is always last (more consistent?):

Operator	Description
=:	equals type (no clash with assignment)
?:	type is (C# is keyword)
<?:	type as (optional cast)
<:	down cast type
>:	up cast type? (is implicit)

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String Operator Symbols

Operators for strings and characters.

Operator	Description
'' ''	Delimiters for a symbol name with special characters.
=~	Case (and culture) insensitive equals.
<>~	Case (and culture) insensitive not-equals.
>~	Case (and culture) insensitive greater-than - compare.
<~	Case (and culture) insensitive lesser-than - compare.
>=~	Case (and culture) insensitive greater-than-or-equal - compare.
=<~	Case (and culture) insensitive lesser-than-or-equal - compare.
s[2..6]	sub-string using Range.
<+	Concat a string*.
/<+	Concat (join) a string with path separator.
"x"<+	Concat (join) a string with any (x) separator?

*) Perhaps concatenation does not require an operator at all? "Hello " "World"

Array operators should also work on string character items.

Comparison Operator with Margin Symbols

Operators for comparing numbers with a margin. Typically useful for floating point numbers but should also work for integers.

Operator	Description
= ~	Equals with a margin.
<> ~	Not equals with a margin.
> ~	Greater than with a margin.
< ~	Lesser than with a margin.
>= ~	Greater-than-or-equal.
=< ~	Lesser-than-or-equal.

These operators require 3 operands.

f := 3.14
pi := 3.1415

// how to specify three operands?
if f = pi ~ 0.01
    // same (within margin)

Also applicable to dates:

now := DateTime.Now
d := DateTime.Now.AddDays(1)    // just some date

if f = now ~ TimeSpan.FromMinutes(1)
    // same (within margin)

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Array and List operators

Operators for working with Array<T> and List<T> types.

Any arithmetic operator also works on arrays and lists. Operators starting with < indicates a structural operation, like adding or removing elements from an array/list.

TBD: Do we also support comparison and logical operators that result in an array of booleans? What about set operators (union etc.)? What happens (arithmetic) if arrays are not of the same size?

Operator	Description
+	adds the values of each element of two array/lists together.
-	subtracts the values from each element of two array/lists.
x	x = any arithmetic operator that acts on each element of the two array/lists.
+=	mutable - add a value to all array/list elements
-=	mutable - subtract a value from all array/list elements
*=	mutable - multiply a value with all array/list elements
x=	mutable - x = any arithmetic operator acts on all elements of the array/list
<+	add item(s) to the end of an array/list (concat)
<-	remove item(s) from anywhere in array/list (first exact match)
<^	insert item(s) into array/list (front)
<&	add item(s) to array/list/tree as a child (?)
<\|	insert item(s) to the front of an array/list/tree as a child (?)
<+=	mutable - add item(s) to the end of an array/list (concat)
<-=	mutable - remove item(s) from anywhere in array/list (first exact match)
<^=	mutable - insert item(s) into array/list (front)
<&=	mutable - add item(s) to array/list/tree as a child (?)
<\|=	mutable - insert item(s) to the front of an array/list/tree as a child (?)
in	test if item(s) is in array/list (contains)
not in	test if item(s) is not in array/list (not contains)
</	split in array with chunks/tuples of n
<\|	zip two arrays
<~	unzip (split)
.>	Collect the property values on all instances in the array
[..]	Range operator returns a sub array/list.
[i]	Index (i) operator returns a single item.
[?i]	Safe index (i) operator returns an optional single item.
[*]	returns the enumerator of an array/list.
[**]	returns the parallel enumerator of an array/list.
[**/n]	returns the parallel enumerator of an array/list for max n-threads.
[**%n]	returns the parallel enumerator of an array/list with n-elements in each thread.

arr1 := (1, 2, 3, 4, 5)
arr2 := (5, 4, 3, 2, 1)

arr3 := arr1 + arr2
// arr3 = (6, 6, 6, 6, 6)

arr1 <+= 42      // arr1 = (1, 2, 3, 4, 5, 42)
arr2 <^= 101     // arr2 = (101, 5, 4, 3, 2, 1)

arr4 := arr1 + arr2
// arr4 = (102, 7, 7, 7, 7, 43)

arr := (1, 2, 3, 4, 5)
// add single item
arr2 := arr <+ 6   // arr2 = (1, 2, 3, 4, 5, 6)
// remove multiple items - whole array must match!
arr3 := arr <- (1, 2, 3)    // arr3 = (4, 5, 6)
// arr is unchanged

// contains
b := 4 in arr            // true
c := (2, 4) not in arr   // true

Special collection operator for accessing the same property on an array of objects.

Person
    Name: Str
    Age: U8

arr: Array<Person> = (...)

// returns the names of all persons in the array
names := arr.>Name
// names: Array<Str>

// Collect multiple properties?
people := arr.>Name, arr.>Age
people := { Name = arr.>Name, Age = arr.>Age }
// people: Array<{Str, U8}>

// Does it work the same with functions?

fn: (self: Person): Str
    return "$self.Name is $self.Age years old."

// returns "'name' is 'age' years old." for all persons in the array
names := arr.>fn

// Do we allow more function parameters?

fn: (self: Person, magic: U8): Str
    return "$self.Name called with $magic."

// calls fn with magic=42 for all persons in the array
names := arr.>fn(42)
// How to make it clear 42 is duplicated to all calls!? Use of '.>'?

TBD: Allow ‘array programming’ operator (overloads) that target simd instructions?

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Mutating Operators

All these operators work as follows: Read left, [op] right to left, write left

These operators cannot be overloaded, they simply use the standard operators.

Operator	Description
+=	read (left) - add (right to left) - write (left)
-=	read - subtract - write
*=	read - multiply - write
/=	read - divide - write
%=	read - modulo/remainder - write
**=	read - power - write
>>=	read - shift right - write
<<=	read - shift left - write
>\|=	read - roll right - write
\|<=	read - roll left - write
?=	read - test - write (locking?)
!=	read - error?? - write
&=	read - bit and - write
\|=	read - bit or - write
^=	read - bit xor - write
$=	read - ?? - write
^=	read - ‘immutable’ ?? - write
\|>=	?
<\|=	? (or =<\|)

TBD: Some of these could be interlocked.

What syntax to use? |+=|, \\+=

Operator	Description
\|+=\|	interlocked (read - add - write)
\|-=\|	interlocked (read - subtract - write)

Do we allow a list of right values? (yes)

a :=^ 42    // mutable
a += (12, 23, 34)
// a = a + 12 + 23 + 34

a += (x, y, z)

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Data Type Wrapper Conversion Assignment Operators

Goal is to have a quick and easy way to convert from a normal data type T to one of the wrapper types (of T). Note the type-operator is on the right side of the equals sign.

TBD: Should we add a : to the syntax to indicate it is about types? opt =:? x

Operator	Description
=!	Err<T> = T
=?	Opt<T> = T
=*	Ptr<T> = T (Ptr() conversion)
=^	Mut<T> = T
=%	Atom<T> = T

a: U8 = 42
err =! a    // err: Err<U8>
opt =? a    // opt: Opt<U8>
ptr =* a    // ptr: Ptr<U8>
mut =^ a    // mut: Mut<U8>
atom =% a    // atom: Atom<U8>

// as parameters inline
fnErr(!a)
fnOpt(?a)
fnPtr(*a)
fnImm(^a)
fnAtom(%a)

// or named parameters
fnErr(err =! a)
fnOpt(opt =? a)
fnPtr(ptr =* a)
fnImm(imm =^ a)
fnAtom(imm =% a)

Or are these conversions implicit?

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What if operators cause overflow (or underflow)? A bitwise shift << can shift out bits - sort of the point. Does every operator determine for itself if overflow is a problem or is there a general principle?

What syntax to specifically use/call checked or unchecked operator implementations? How to ignore overflow?

See TBD note at the top about checked, wrap around and saturate operators.

a := 42
// checked on U16 target by default
x: U16 = a ** a

// use explicit conversion overload?
x: U16 = U16(a ** a, .Unchecked)

// use explicit conversion function?
x: U16 = U16unchecked(a ** a)

// unchecked operator?
x: U16 = $(a ** a)
x: U16 = !(a ** a)

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TBD

• allow custom defined operators? .>>., |<< etc. Requires identifiers to be less strict. Also requires escape characters in function definition symbol: ''.>>.'': (...): Bool. The names would be considered normal functions and therefor -to be used as operators- would need to adhere to the infix function rules.

Then there is also a .NET interop problem. How are these operators exposed to (for instance) a C# program? We could spell out each character to make a unique name that is still callable from other .NET languages.

• ’.>>.’ => op_dotgtgtdot
• ’|<<’ => op_pipeltlt

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TBD: Is operator overloading useful for operators other than arithmetic, comparable and possibly logical?

Which operators will definitely not be overloadable?

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TBD

Implement operators by tagging regular functions with the operator signs. This seems to be the best way to also interop with normal .NET / C#.

// must follow the infix function rules.
[[BinaryOperator(">>|")]]
MyWeirdOperator: <T>(self: T, other: T): T
    ...

a := 42
x := a >>| 101   // calls MyWeirdOperator

// How to do unary or ternary operators?
[[UnaryOperator("-")]]
MyUnaryOperator: <T>(other: T): T

[[TernaryOperator(">>|", "|<<")]]
MyTernaryOperator: <T>(self: T, other: T, third: T): T