isRecord: add variant with a label

preserves.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version = "20221025"
+version = "20221027"
 author        = "Emery Hemingway"
 description   = "data model and serialization format"
 license       = "Unlicense"

src/preserves.nim

@@ -391,9 +391,23 @@ func isSymbol*(pr: Preserve; sym: string|Symbol): bool {.inline.} =
   ## Check if ``pr`` is a Preserves symbol of ``sym``.
   (pr.kind == pkSymbol) and (pr.symbol == Symbol(sym))
 
+proc label*(pr: Preserve): Preserve {.inline.} =
+  ## Return the label of record value.
+  pr.record[pr.record.high]
+
+proc arity*(pr: Preserve): int {.inline.} =
+  ## Return the number of fields in record `pr`.
+  pred(pr.record.len)
+
 func isRecord*(pr: Preserve): bool {.inline.} = (pr.kind == pkRecord) and (pr.record.len > 0)
   ## Check if ``pr`` is a Preserves record.
 
+func isRecord*(pr: Preserve; label: string): bool {.inline.} =
+  ## Check if ``pr`` is a Preserves record with the given label symbol.
+  pr.kind == pkRecord and
+    pr.record.len > 0 and
+    pr.label.isSymbol(label)
+
 proc isSequence*(pr: Preserve): bool {.inline.} = pr.kind == pkSequence
   ## Check if ``pr`` is a Preserves sequence.
 
@@ -408,14 +422,6 @@ func isEmbedded*[E](pr: Preserve[E]): bool {.inline.} =
   when E is void: pr.embedded # embedded Preserves
   else: pr.kind == pkEmbedded # embedded Nim
 
-proc label*(pr: Preserve): Preserve {.inline.} =
-  ## Return the label of record value.
-  pr.record[pr.record.high]
-
-proc arity*(pr: Preserve): int {.inline.} =
-  ## Return the number of fields in record `pr`.
-  pred(pr.record.len)
-
 proc fields*(pr: Preserve): seq[Preserve] {.inline.} =
   ## Return the fields of a record value.
   pr.record[0..pr.record.high.pred]