Improved float parsing

* Fixed #30
 * Accept underscores in float literals
 * Added test

test/tserialization.nim

@@ -5,7 +5,7 @@
 #    distribution, for details about the copyright.
 
 import "../yaml"
-import unittest, strutils, streams, tables, times
+import unittest, strutils, streams, tables, times, math
 
 type
   MyTuple = tuple
@@ -197,6 +197,15 @@ suite "Serialization":
     load(input, result)
     assert(result == 14)
 
+  test "Load floats":
+    let input = "[6.8523015e+5, 685.230_15e+03, 685_230.15, -.inf, .NaN]"
+    var result: seq[float]
+    load(input, result)
+    for i in 0..2:
+      assert result[i] == 6.8523015e+5
+    assert result[3] == NegInf
+    assert classify(result[4]) == fcNan
+
   test "Load nil string":
     let input = newStringStream("!<tag:nimyaml.org,2016:nil:string> \"\"")
     var result: string

yaml/hints.nim

@@ -124,6 +124,9 @@ template advanceTypeHint(ch: char) {.dirty.} =
     ythMonth1                 => ythMonthMinusNoYmd
     ythMonth2                 => ythMonthMinus
     [ythFraction, ythSecond2] => ythAfterTimePlusMinus
+  of '_':
+    [ythInt1, ythInt2, ythInt3, ythInt4] => ythInt
+    [ythInt, ythDecimal] => nil
   of ':':
     [ythHour1, ythHour2]      => ythHourColon
     ythMinute2                => ythMinuteColon

yaml/serialization.nim

@@ -16,7 +16,7 @@
 ## type. Please consult the serialization guide on the NimYAML website for more
 ## information.
 
-import tables, typetraits, strutils, macros, streams, times
+import tables, typetraits, strutils, macros, streams, times, parseutils
 import parser, taglib, presenter, stream, ../private/internal, hints
 export stream
   # *something* in here needs externally visible `==`(x,y: AnchorId),
@@ -138,7 +138,8 @@ template constructScalarItem*(s: var YamlStream, i: untyped,
   except YamlConstructionError: raise
   except Exception:
     var e = constructionError(s,
-        "Cannot construct to " & name(t) & ": " & item.scalarContent)
+        "Cannot construct to " & name(t) & ": " & item.scalarContent &
+        "; error: " & getCurrentExceptionMsg())
     e.parent = getCurrentException()
     raise e