System built-ins
Flux contains many preassigned values. These preassigned values are defined in the source files for the various built-in packages.
When a built-in value is not expressible in Flux, its value may be defined by the hosting environment. All such values must have a corresponding builtin statement to declare the existence and type of the built-in value.
BuiltinStatement = "builtin" identifier ":" TypeExpression .
TypeExpression = MonoType ["where" Constraints] .
MonoType = Tvar | BasicType | ArrayType | StreamType | VectorType | RecordType | FunctionType .
Tvar = "A" … "Z" .
BasicType = "int" | "uint" | "float" | "string" | "bool" | "time" | "duration" | "bytes" | "regexp" .
ArrayType = "[" MonoType "]" .
StreamType = "stream" "[" MonoType "]" .
VectorType = "vector" "[" MonoType "]" .
RecordType = ( "{" [RecordTypeProperties] "}" ) | ( "{" Tvar "with" RecordTypeProperties "}" ) .
FunctionType = "(" [FunctionTypeParameters] ")" "=>" MonoType .
RecordTypeProperties = RecordTypeProperty { "," RecordTypeProperty } .
RecordTypeProperty = Label ":" MonoType .
Label = identifier | string_lit
FunctionTypeParameters = FunctionTypeParameter { "," FunctionTypeParameter } .
FunctionTypeParameter = [ "<-" | "?" ] identifier ":" MonoType .
Constraints = Constraint { "," Constraint } .
Constraint = Tvar ":" Kinds .
Kinds = identifier { "+" identifier } .Example
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