ME005: RESULT + OPTION COMPOSITION (SAFE LOOKUP + PARSE)

---
{
  "@context": "https://nxdlang.org/schema",
  "doc_id": "ME005",
  "title": "",
  "description": "",
  "layer": "Examples",
  "category": "Medium Examples",
  "keywords": [],
  "doc_version": "1.0",
  "status": "active"
}
---


# ME005: RESULT + OPTION COMPOSITION (SAFE LOOKUP + PARSE)

### NXD
```nxd
MODULE error.composition

TYPE OPTION UNION { SOME(any), NONE }
TYPE RESULT UNION { OK(any), ERR(string) }

LET CONFIG SET MAP<string, string> {
    "port": "8080",
    "host": "localhost"
}

FUNC GET_CONFIG(KEY: string): OPTION:
    IF CONFIG HAS KEY:
        RETURN SOME(CONFIG[KEY])
    RETURN NONE

FUNC PARSE_INT(S: string): RESULT:
    IF S CONTAINS NON_DIGIT:
        RETURN ERR("not numeric")
    RETURN OK(S AS int)

FUNC GET_PORT(): RESULT:
    MATCH GET_CONFIG("port"):
        CASE SOME(V):
            RETURN PARSE_INT(V)
        CASE NONE:
            RETURN ERR("missing port")

FUNC MAIN():
    LET R SET GET_PORT()
    MATCH R:
        CASE OK(P):
            PRINTLN("port: " ADD P)
        CASE ERR(E):
            PRINTLN("error: " ADD E)
    RETURN NONE
```