Replace concat with writeText

Write to a stream rather than concatentate a string.

src/preserves.nim

@@ -1188,80 +1188,84 @@ proc mapEmbeds*[A, B](pr: sink Preserve[A]; op: proc (v: A): B): Preserve[B] =
     of pkEmbedded:
       result = embed op(pr.embed)
 
-proc concat[E](result: var string; pr: Preserve[E]) =
-  if pr.embedded: result.add("#!")
+proc writeText*[E](stream: Stream; pr: Preserve[E]) =
+  ## Encode Preserves to a `Stream` as text.
+  if pr.embedded: write(stream, "#!")
   case pr.kind:
   of pkBoolean:
     case pr.bool
-    of false: result.add "#f"
-    of true: result.add "#t"
+    of false: write(stream, "#f")
+    of true: write(stream, "#t")
   of pkFloat:
-    result.add($pr.float & "f")
+    write(stream, $pr.float)
+    write(stream, 'f')
   of pkDouble:
-    result.add $pr.double
+    write(stream, $pr.double)
   of pkSignedInteger:
-    result.add $pr.int
+    write(stream, $pr.int)
   of pkString:
-    result.add escapeJson(pr.string)
+    write(stream, escapeJson(pr.string))
   of pkByteString:
     if pr.bytes.allIt(char(it) in {' '..'!', '#'..'~'}):
-      result.add("#\"")
-      result.add(cast[string](pr.bytes))
-      result.add('"')
+      write(stream, "#\"")
+      write(stream, cast[string](pr.bytes))
+      write(stream, '"')
     else:
       if pr.bytes.len > 64:
-        result.add("#[") #]#
-        result.add(base64.encode(pr.bytes))
-        result.add(']')
+        write(stream, "#[") #]#
+        write(stream, base64.encode(pr.bytes))
+        write(stream, ']')
       else:
         const alphabet = "0123456789abcdef"
-        result.add("#x\"")
+        write(stream, "#x\"")
         for b in pr.bytes:
-          result.add(alphabet[int(b shr 4)])
-          result.add(alphabet[int(b and 0xf)])
-        result.add('"')
+          write(stream, alphabet[int(b shr 4)])
+          write(stream, alphabet[int(b and 0xf)])
+        write(stream, '"')
   of pkSymbol:
-    result.add(escapeJsonUnquoted(string pr.symbol))
+    write(stream, escapeJsonUnquoted(string pr.symbol))
   of pkRecord:
     assert(pr.record.len > 0)
-    result.add('<')
-    result.concat(pr.record[pr.record.high])
+    write(stream, '<')
+    writeText(stream, pr.record[pr.record.high])
     for i in 0..<pr.record.high:
-      result.add(' ')
-      result.concat(pr.record[i])
-    result.add('>')
+      write(stream, ' ')
+      writeText(stream, pr.record[i])
+    write(stream, '>')
   of pkSequence:
-    result.add('[')
-    for i, val in pr.sequence:
-      if i > 0: result.add(' ')
-      result.concat(val)
-    result.add(']')
+    write(stream, '[')
+    var insertWhitespace: bool
+    for val in pr.sequence:
+      if insertWhitespace: write(stream, ' ')
+      else: insertWhitespace = true
+      writeText(stream, val)
+    write(stream, ']')
   of pkSet:
-    result.add("#{")
+    write(stream, "#{")
+    var insertWhitespace: bool
     for val in pr.set.items:
-      result.concat(val)
-      result.add(' ')
-    if pr.set.len > 1:
-      result.setLen(result.high)
-    result.add('}')
+      if insertWhitespace: write(stream, ' ')
+      else: insertWhitespace = true
+      writeText(stream, val)
+    write(stream, '}')
   of pkDictionary:
-    result.add('{')
-    var i = 0
+    write(stream, '{')
+    var insertWhitespace: bool
     for (key, value) in pr.dict.items:
-      if i > 0:
-        result.add(' ')
-      result.concat(key)
-      result.add(": ")
-      result.concat(value)
-      if i < pr.dict.high:
-        result.add(',')
-      inc i
-    result.add('}')
+      if insertWhitespace: write(stream, ' ')
+      else: insertWhitespace = true
+      writeText(stream, key)
+      write(stream, ": ")
+      writeText(stream, value)
+    write(stream, '}')
   of pkEmbedded:
-    result.add("#!")
-    result.add($pr.embed)
+    write(stream, "#!")
+    write(stream, $pr.embed)
 
-proc `$`*(pr: Preserve): string = concat(result, pr)
+proc `$`*[E](pr: Preserve[E]): string =
   ## Generate the textual representation of ``pr``.
+  var stream = newStringStream()
+  writeText(stream, pr)
+  result = move stream.data
 
 include ./preserves/private/parse

tests/test_conversions.nim

@@ -35,7 +35,7 @@ suite "conversions":
     var a: Table[int, string]
     for i, s in ["a", "b", "c"]: a[i] = s
     let b = toPreserve(a)
-    check($b == """{0: "a", 1: "b", 2: "c"}""")
+    check($b == """{0: "a" 1: "b" 2: "c"}""")
     var c: Table[int, string]
     check(fromPreserve(c, b))
     check(a == c)