Various improvements

* Better JSON serialization (map bool literals to true/false if
   possible)
 * Fixed a problem where the tag of block sequence would be
   wrongly placed
 * Always output "" when dumping empty strings
 * Added helper functions to create YamlStreamEvents.
 * Moved procs for YamlStreamEvents to private/events.nim
 * renamed dump() to present()
 * Added dump() and load() to yaml.serialization

private/dumper.nim

@@ -13,8 +13,9 @@ type
         dFlowSequenceStart
 
 proc needsEscaping(scalar: string): bool =
-    scalar.find({'{', '}', '[', ']', ',', '#', '-', ':', '?', '%', '\x0A',
-                 '\c'}) != -1
+    scalar.len == 0 or 
+            scalar.find({'{', '}', '[', ']', ',', '#', '-', ':', '?', '%',
+                         '\x0A', '\c'}) != -1
 
 proc writeDoubleQuoted(scalar: string, s: Stream) =
     s.write('"')
@@ -116,8 +117,8 @@ proc writeTagAndAnchor(target: Stream, tag: TagId, tagLib: YamlTagLibrary,
         target.write(cast[byte]('a') + cast[byte](anchor))
         target.write(' ')
 
-proc dump*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
-           style: YamlDumpStyle = yDumpDefault, indentationStep: int = 2) =
+proc present*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
+              style: YamlDumpStyle = yDumpDefault, indentationStep: int = 2) =
     var
         cached = initQueue[YamlStreamEvent]()
         cacheIterator = iterator(): YamlStreamEvent =
@@ -147,8 +148,20 @@ proc dump*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
                 writeTagAndAnchor(target,
                                   item.scalarTag, tagLib, item.scalarAnchor)
             
-            if item.scalarContent.needsEscaping or
-               style in [yDumpCanonical, yDumpJson]:
+            if (style == yDumpJson and item.scalarTag in [yTagQuestionMark,
+                                                          yTagBoolean] and
+                    item.scalarType in [yTypeBoolTrue, yTypeBoolFalse]):
+                if item.scalarType == yTypeBoolTrue:
+                    target.write("true")
+                else:
+                    target.write("false")
+            elif style == yDumpCanonical or item.scalarContent.needsEscaping or
+               (style == yDumpJson and
+                (item.scalarTag notin [yTagQuestionMark, yTagInteger, yTagFloat,
+                                       yTagBoolean, yTagNull] or
+                 (item.scalarTag == yTagQuestionMark and item.scalarType notin
+                  [yTypeBoolFalse, yTypeBoolTrue, yTypeInteger, yTypeFloat,
+                   yTypeNull]))):
                 writeDoubleQuoted(item.scalarContent, target)
             else:
                 target.write(item.scalarContent)
@@ -193,21 +206,15 @@ proc dump*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
                                           item.seqTag, tagLib, item.seqAnchor)
                 else:
                     if style != yDumpJson:
-                        target.write('\x0A')
                         writeTagAndAnchor(target,
                                           item.seqTag, tagLib, item.seqAnchor)
+                    target.write('\x0A')
                     indentation += indentationStep
             else:
-                if nextState == dBlockSequenceItem:
-                    if style != yDumpJson:
-                        writeTagAndAnchor(target,
-                                          item.seqTag, tagLib, item.seqAnchor)
-                    startItem(target, style, indentation, levels[levels.high])
-                else:
-                    startItem(target, style, indentation, levels[levels.high])
-                    if style != yDumpJson:
-                        writeTagAndAnchor(target,
-                                          item.seqTag, tagLib, item.seqAnchor)
+                startItem(target, style, indentation, levels[levels.high])
+                if style != yDumpJson:
+                    writeTagAndAnchor(target,
+                                      item.seqTag, tagLib, item.seqAnchor)
                 indentation += indentationStep
             
             if nextState == dFlowSequenceStart:
@@ -267,7 +274,8 @@ proc dump*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
                     indentation += indentationStep
             else:
                 if nextState in
-                        [dBlockExplicitMapValue, dBlockImplicitMapValue]:
+                        [dBlockExplicitMapValue, dBlockImplicitMapValue,
+                         dBlockImplicitMapKey]:
                     if style != yDumpJson:
                         writeTagAndAnchor(target,
                                           item.mapTag, tagLib, item.mapAnchor)
@@ -368,5 +376,5 @@ proc transform*(input: Stream, output: Stream, style: YamlDumpStyle,
     var
         tagLib = extendedTagLibrary()
         parser = newParser(tagLib)
-    dump(parser.parse(input), output, tagLib, style,
-         indentationStep)
+    present(parser.parse(input), output, tagLib, style,
+            indentationStep)

private/sequential.nim

@@ -29,6 +29,28 @@ type
     BlockScalarStyle = enum
         bsLiteral, bsFolded
 
+proc `$`*(id: TagId): string =
+    case id
+    of yTagQuestionMark: "?"
+    of yTagExclamationMark: "!"
+    of yTagString: "!!str"
+    of yTagSequence: "!!seq"
+    of yTagMap: "!!map"
+    of yTagNull: "!!null"
+    of yTagBoolean: "!!bool"
+    of yTagInteger: "!!int"
+    of yTagFloat: "!!float"
+    of yTagOrderedMap: "!!omap"
+    of yTagPairs: "!!pairs"
+    of yTagSet: "!!set"
+    of yTagBinary: "!!binary"
+    of yTagMerge: "!!merge"
+    of yTagTimestamp: "!!timestamp"
+    of yTagValue: "!!value"
+    of yTagYaml: "!!yaml"
+    else:
+        "<" & $cast[int](id) & ">"
+
 proc newParser*(tagLib: YamlTagLibrary): YamlSequentialParser =
     new(result)
     result.tagLib = tagLib
@@ -40,55 +62,6 @@ proc anchor*(parser: YamlSequentialParser, id: AnchorId): string =
             return pair[0]
     return nil
         
-proc `==`*(left: YamlStreamEvent, right: YamlStreamEvent): bool =
-    if left.kind != right.kind:
-        return false
-    case left.kind
-    of yamlStartDocument, yamlEndDocument, yamlEndMap, yamlEndSequence:
-        result = true
-    of yamlStartMap:
-        result = left.mapAnchor == right.mapAnchor and
-                 left.mapTag == right.mapTag
-    of yamlStartSequence:
-        result = left.seqAnchor == right.seqAnchor and
-                 left.seqTag == right.seqTag
-    of yamlScalar:
-        result = left.scalarAnchor == right.scalarAnchor and
-                 left.scalarTag == right.scalarTag and
-                 left.scalarContent == right.scalarContent and
-                 left.scalarType == right.scalarType
-    of yamlAlias:
-        result = left.aliasTarget == right.aliasTarget
-    of yamlError, yamlWarning:
-        result = left.description == right.description and
-                 left.line == right.line and left.column == right.column
-
-proc `$`*(event: YamlStreamEvent): string =
-    result = $event.kind & '('
-    case event.kind
-    of yamlEndMap, yamlEndSequence, yamlStartDocument, yamlEndDocument:
-        discard
-    of yamlStartMap:
-        result &= "tag=" & $event.mapTag
-        if event.mapAnchor != yAnchorNone:
-            result &= ", anchor=" & $event.mapAnchor
-    of yamlStartSequence:
-        result &= "tag=" & $event.seqTag
-        if event.seqAnchor != yAnchorNone:
-            result &= ", anchor=" & $event.seqAnchor
-    of yamlScalar:
-        result &= "tag=" & $event.scalarTag
-        if event.scalarAnchor != yAnchorNone:
-            result &= ", anchor=" & $event.scalarAnchor
-        result &= ", typeHint=" & $event.scalarType
-        result &= ", content=\"" & event.scalarContent & '\"'
-    of yamlAlias:
-        result &= "aliasTarget=" & $event.aliasTarget
-    of yamlWarning, yamlError:
-        result &= "line=" & $event.line & ", column=" & $event.column
-        result &= ", description=\"" & event.description & '\"'
-    result &= ")"
-        
 template yieldWarning(d: string) {.dirty.} =
     yield YamlStreamEvent(kind: yamlWarning, description: d,
                           line: lex.line, column: lex.column)

test/serializing.nim

@@ -26,8 +26,7 @@ suite "Serialization":
     test "Serialize string sequence":
         var input = @["a", "b"]
         var output = newStringStream()
-        dump(wrapWithDocument(serialize(input)), output, coreTagLibrary(),
-             yDumpBlockOnly)
+        dump(input, output, yDumpBlockOnly)
         assert output.data == "%YAML 1.2\n--- \n- a\n- b"
     
     test "Load Table[int, string]":
@@ -47,8 +46,7 @@ suite "Serialization":
         input[23] = "dreiundzwanzig"
         input[42] = "zweiundvierzig"
         var output = newStringStream()
-        dump(wrapWithDocument(serialize(input)), output, coreTagLibrary(),
-                yDumpBlockOnly)
+        dump(input, output, yDumpBlockOnly)
         assert output.data == "%YAML 1.2\n--- \n23: dreiundzwanzig\n42: zweiundvierzig"
     
     test "Load Sequences in Sequence":
@@ -67,8 +65,7 @@ suite "Serialization":
     test "Serialize Sequences in Sequence":
         let input = @[@[1, 2, 3], @[4, 5], @[6]]
         var output = newStringStream()
-        dump(wrapWithDocument(serialize(input)), output, coreTagLibrary(),
-                yDumpDefault)
+        dump(input, output, yDumpDefault)
         assert output.data == "%YAML 1.2\n--- \n- [1, 2, 3]\n- [4, 5]\n- [6]"
     
     test "Load custom object":
@@ -86,6 +83,5 @@ suite "Serialization":
     test "Serialize custom object":
         let input = Person(firstname: "Peter", surname: "Pan", age: 12)
         var output = newStringStream()
-        dump(wrapWithDocument(serialize(input)), output, coreTagLibrary(),
-                yDumpBlockOnly)
+        dump(input, output, yDumpBlockOnly)
         assert output.data == "%YAML 1.2\n--- \nfirstname: Peter\nsurname: Pan\nage: 12"

yaml.nim

@@ -85,7 +85,7 @@ type
         ## The value ``mapMayHaveKeyObjects`` is a hint from a serializer and is
         ## used for choosing an appropriate presentation mode for a YAML map
         ## (flow or block, explicit or implicit) by
-        ## `dump <#dump,YamlStream,Stream,YamlTagLibrary,YamlDumpStyle,int>`_.
+        ## `present <#present,YamlStream,Stream,YamlTagLibrary,YamlDumpStyle,int>`_.
         ## If it is set to ``false``, the map may only have scalars as keys.
         ##
         ## The value ``scalarType`` is a hint from the lexer, see
@@ -239,8 +239,22 @@ proc `==`*(left: YamlStreamEvent, right: YamlStreamEvent): bool
 proc `$`*(event: YamlStreamEvent): string
     ## outputs a human-readable string describing the given event
 
+proc startDocEvent*(): YamlStreamEvent {.inline.}
+proc endDocEvent*(): YamlStreamEvent {.inline.}
+proc startMapEvent*(tag: TagId = yTagQuestionMark,
+                    anchor: AnchorId = yAnchorNone,
+                    mayHaveKeyObjects: bool = true): YamlStreamEvent {.inline.}
+proc endMapEvent*(): YamlStreamEvent {.inline.}
+proc startSeqEvent*(tag: TagId = yTagQuestionMark,
+                    anchor: AnchorId = yAnchorNone): YamlStreamEvent {.inline.}
+proc endSeqEvent*(): YamlStreamEvent {.inline.}
+proc scalarEvent*(content: string = "", tag: TagId = yTagQuestionMark,
+                  anchor: AnchorId = yAnchorNone, 
+                  typeHint: YamlTypeHint = yTypeUnknown):
+                  YamlStreamEvent {.inline.}
+
 proc `==`*(left, right: TagId): bool {.borrow.}
-proc `$`*(id: TagId): string {.borrow.}
+proc `$`*(id: TagId): string
 proc hash*(id: TagId): Hash {.borrow.}
 
 proc `==`*(left, right: AnchorId): bool {.borrow.}
@@ -310,8 +324,8 @@ proc constructJson*(s: YamlStream): seq[JsonNode]
     ## check for these values and will output invalid JSON when rendering one
     ## of these values into a JSON character stream.
     
-proc dump*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
-           style: YamlDumpStyle = yDumpDefault, indentationStep: int = 2)
+proc present*(s: YamlStream, target: Stream, tagLib: YamlTagLibrary,
+              style: YamlDumpStyle = yDumpDefault, indentationStep: int = 2)
     ## Convert ``s`` to a YAML character stream and write it to ``target``.
     
 proc transform*(input: Stream, output: Stream, style: YamlDumpStyle,
@@ -323,6 +337,7 @@ proc transform*(input: Stream, output: Stream, style: YamlDumpStyle,
 
 include private.lexer
 include private.tagLibrary
+include private.events
 include private.sequential
 include private.json
 include private.dumper

yaml/serialization.nim

@@ -110,13 +110,6 @@ proc prepend*(event: YamlStreamEvent, s: YamlStream): YamlStream =
         for e in s():
             yield e
 
-proc wrapWithDocument*(s: YamlStream): YamlStream =
-    result = iterator(): YamlStreamEvent =
-        yield YamlStreamEvent(kind: yamlStartDocument)
-        for event in s():
-            yield event
-        yield YamlStreamEvent(kind: yamlEndDocument)
-
 proc construct*(s: YamlStream, result: var string) =
     let item = s()
     if finished(s) or item.kind != yamlScalar:
@@ -278,3 +271,21 @@ proc serialize*[K, V](value: Table[K, V],
             for event in events():
                 yield event
         yield YamlStreamEvent(kind: yamlEndMap)
+
+proc load*[K](input: Stream, target: var K) =
+    var
+        parser = newParser(coreTagLibrary())
+        events = parser.parse(input)
+    assert events().kind == yamlStartDocument
+    construct(events, target)
+    assert events().kind == yamlEndDocument
+
+proc dump*[K](value: K, target: Stream, style: YamlDumpStyle = yDumpDefault,
+              indentationStep: int = 2) =
+    var serialized = serialize(value, style == yDumpCanonical)
+    var events = iterator(): YamlStreamEvent =
+        yield YamlStreamEvent(kind: yamlStartDocument)
+        for event in serialized():
+            yield event
+        yield YamlStreamEvent(kind: yamlEndDocument)
+    present(events, target, coreTagLibrary(), style, indentationStep)