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|---|---|---|
 | Chapter 5. Patterns |  |
| 5.4. List Pattern | 5.5. Record Pattern | 5.6. Call Pattern |
| ||
|---|---|---|
| | Chapter 5. Patterns | |
| 5.4. List Pattern | 5.5. Record Pattern | 5.6. Call Pattern |
When a record pattern is matched against a record value, each key mentioned in the record pattern must have a mapping in the record value, and each such mapped value must match its corresponding pattern. The record value may contain additional keys not mentioned by the record pattern.
When a record pattern {. K0 = P0 , … , Kn = Pn .}
is matched against a record type R, each Ki
must have a binding in R. Then each Pi is
matched against the type bound to Ki in R,
producing a typing context Γi.
The typing context produced by the whole match is the union of the contexts Γi.
{- Use records to test for a given string -} val applicants = [ {. name = "Harry Q. Bovik", college = "Carnegie Mellon University", status = "accepted" .}, {. name = "Fred Hacker", college = "Massachusetts Institute of Technology", status = "rejected" .}, {. name = "D. F. Automaton", college = "Final State College", status = "accepted" .} ] each(applicants) >a> ( a >{. name = n, status = "accepted" .}> Println(n + "'s application was accepted") >> stop | a >{. name = n, status = "rejected" .}> Println(n + "'s application was not accepted") >> stop ) {- OUTPUT:PERMUTABLE Fred Hacker's application was not accepted D. F. Automaton's application was accepted Harry Q. Bovik's application was accepted -}