sum_type

form a union of named types from a map

Synopsis

sum_type(m: map{string:type}) -> type

Description

The sum_type function returns a union type whose members are named types, one for each entry of the map m, where each entry’s key is the name and its value is the type, i.e., sum_type(map{"A":<T1>,"B":<T2>}) is <A=T1|B=T2>. This forms a sum type (or tagged union), where the name of each member identifies its variant even when two variants have the same underlying type.

If m has a single entry, sum_type returns its named type.

If a key of m is already bound to a different type, an error is returned.

Examples

Form a sum type from a map of types

# spq
values sum_type(this)
# input
map{"Circle":<{radius:float64}>,"Rect":<{width:float64,height:float64}>}
# expected output
type Circle={radius:float64}
type Rect={width:float64,height:float64}
<Circle|Rect>

Compute a sum type of events from their fused types

# spq
fuse(this) by kind
| collect_map(map{kind:fuse})
| values sum_type(this)
# input
{kind:"Push",ref:"main"}
{kind:"Watch",action:"started"}
{kind:"Push",ref:"dev"}
# expected output
type Push={kind:string,ref:string}
type Watch={kind:string,action:string}
<Push|Watch>