Add support for enumerated values

[jeromesimeon]

Ergo should allow for creations of enum values. This relies on the ability to read/import CTO files.

[jeromesimeon]

This requires #9 #10

[jeromesimeon]

Some notes about how enum types and values can be encoded into Ergo's internal notion of types and values.

Enum types are encoded as branded sum types:

enum Gender {
  o MALE
  o FEMALE
  o OTHER
  o UNKNOWN
}
==
Brand Gender {
  Either String
    (Either String
      (Either String
        String))

This encoding should provide for accurate type checking. There will be challenges in providing good error reporting for those. Most likely the compilation context should maintain a table of declared enum types.

Enum values are encoded as branded sum values:

MALE    == dbrand Gender (dleft "MALE")
FEMALE  == dbrand Gender (dright (dleft "FEMALE"))
OTHER   == dbrand Gender (dright (dright (dleft "OTHER")))
UNKNOWN == dbrand Gender (dright (dright (dright "UNKNOWN")))

From value to JSON:

MALE
==
{ "$class": "Gender",
  "$kind": "enum",
  { "left": "MALE" } }
FEMALE
==
{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "left" : "FEMALE" } } }
OTHER
==
{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "right" : { "left" : "OTHER" } } } }
UNKOWN
==
{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "right" : { "right" : "UNKNOWN" } } } }

toString(data) in REPL

dbrand Gender (dright (dleft "FEMALE"))
-->
FEMALE

toString(data) in JavaScript runtime

{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "left" : "FEMALE" } } }
-->
"FEMALE"

[jeromesimeon]

Some notes about internal enum encoding, for historical preservation.

Some notes about how enum types and values can be encoded into Ergo's internal notion of types and values.

Enum types are encoded as branded sum types:

enum Gender {
  o MALE
  o FEMALE
  o OTHER
  o UNKNOWN
}
==
Brand Gender {
  Either String
    (Either String
      (Either String
        String))

This encoding should provide for accurate type checking. There will be challenges in providing good error reporting for those. Most likely the compilation context should maintain a table of declared enum types.

Enum values are encoded as branded sum values:

MALE    == dbrand Gender (dleft "MALE")
FEMALE  == dbrand Gender (dright (dleft "FEMALE"))
OTHER   == dbrand Gender (dright (dright (dleft "OTHER")))
UNKNOWN == dbrand Gender (dright (dright (dright "UNKNOWN")))

From value to JSON:

MALE
==
{ "$class": "Gender",
  "$kind": "enum",
  { "left": "MALE" } }
FEMALE
==
{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "left" : "FEMALE" } } }
OTHER
==
{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "right" : { "left" : "OTHER" } } } }
UNKOWN
==
{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "right" : { "right" : "UNKNOWN" } } } }

toString(data) in REPL

dbrand Gender (dright (dleft "FEMALE"))
-->
FEMALE

toString(data) in JavaScript runtime

{ "$class": "Gender",
  "$kind": "enum",
  { "right": { "left" : "FEMALE" } } }
-->
"FEMALE"

[jeromesimeon]

Based on that encoding, with a lot of additional work (notably, enum values are translated as constants), there is a full implementation in https://github.com/accordproject/ergo/tree/js-feature-dynamic-templates