improve runnableExamples and docs for std/nre (#18634)

* improve runnableExamples and docs for std/nre

* avoid too long lines in example

lib/impure/nre.nim

@@ -23,12 +23,12 @@ when defined(js):
 ## **Note**: If you love `sequtils.toSeq` we have bad news for you. This
 ## library doesn't work with it due to documented compiler limitations. As
 ## a workaround, use this:
-##
+runnableExamples:
-## .. code-block:: nim
+  # either `import std/nre except toSeq` or fully qualify `sequtils.toSeq`:
-##
+  import std/sequtils
-##    import std/nre except toSeq
+  iterator iota(n: int): int =
-##
+    for i in 0..<n: yield i
-##
+  assert sequtils.toSeq(iota(3)) == @[0, 1, 2]
 ## Licencing
 ## ---------
 ##
@@ -36,33 +36,28 @@ when defined(js):
 ## this module.
 ##
 ## .. _`some additional terms`: http://pcre.sourceforge.net/license.txt
-##
 runnableExamples:
+  import std/sugar
   let vowels = re"[aeoui]"
-
+  let bounds = collect:
-  let expectedResults = [
+    for match in "moiga".findIter(vowels): match.matchBounds
-    1 .. 1,
+  assert bounds == @[1 .. 1, 2 .. 2, 4 .. 4]
-    2 .. 2,
+  from std/sequtils import toSeq
-    4 .. 4,
+  let s = sequtils.toSeq("moiga".findIter(vowels))
-    6 .. 6,
+    # fully qualified to avoid confusion with nre.toSeq
-    7 .. 7,
+  assert s.len == 3
-  ]
-  var i = 0
-  for match in "moigagoo".findIter(vowels):
-    doAssert match.matchBounds == expectedResults[i]
-    inc i
 
   let firstVowel = "foo".find(vowels)
   let hasVowel = firstVowel.isSome()
-  if hasVowel:
+  assert hasVowel
   let matchBounds = firstVowel.get().captureBounds[-1]
-    doAssert matchBounds.a == 1
+  assert matchBounds.a == 1
 
-  ## as with module `re`, unless specified otherwise, `start` parameter in each
+  # as with module `re`, unless specified otherwise, `start` parameter in each
-  ## proc indicates where the scan starts, but outputs are relative to the start
+  # proc indicates where the scan starts, but outputs are relative to the start
-  ## of the input string, not to `start`:
+  # of the input string, not to `start`:
-  doAssert find("uxabc", re"(?<=x|y)ab", start = 1).get.captures[-1] == "ab"
+  assert find("uxabc", re"(?<=x|y)ab", start = 1).get.captures[-1] == "ab"
-  doAssert find("uxabc", re"ab", start = 3).isNone
+  assert find("uxabc", re"ab", start = 3).isNone
 
 from pcre import nil
 import nre/private/util
@@ -145,7 +140,7 @@ type
     ## `DOLLAR_ENDONLY`, `FIRSTLINE`, `NO_AUTO_CAPTURE`,
     ## `JAVASCRIPT_COMPAT`, `U`, `NO_STUDY`. In other PCRE wrappers, you
     ## will need to pass these as separate flags to PCRE.
-    pattern*: string  ## not nil
+    pattern*: string
     pcreObj: ptr pcre.Pcre  ## not nil
     pcreExtra: ptr pcre.ExtraData  ## nil
 
@@ -165,21 +160,12 @@ type
     ##     the string value of whatever was captured at that id. If the value
     ##     is invalid, then behavior is undefined. If the id is `-1`, then
     ##     the whole match is returned. If the given capture was not matched,
-    ##     `nil` is returned.
+    ##     `nil` is returned. See examples for `match`.
-    ##
-    ##     -  `"abc".match(re"(\w)").get.captures[0] == "a"`
-    ##     -  `"abc".match(re"(?<letter>\w)").get.captures["letter"] == "a"`
-    ##     -  `"abc".match(re"(\w)\w").get.captures[-1] == "ab"`
     ##
     ## `captureBounds[]: HSlice[int, int]`
     ##     gets the bounds of the given capture according to the same rules as
     ##     the above. If the capture is not filled, then `None` is returned.
-    ##     The bounds are both inclusive.
+    ##     The bounds are both inclusive.  See examples for `match`.
-    ##
-    ##     -  `"abc".match(re"(\w)").get.captureBounds[0] == 0 .. 0`
-    ##     -  `0 in "abc".match(re"(\w)").get.captureBounds == true`
-    ##     -  `"abc".match(re"").get.captureBounds[-1] == 0 .. -1`
-    ##     -  `"abc".match(re"abc").get.captureBounds[-1] == 0 .. 2`
     ##
     ## `match: string`
     ##     the full text of the match.
@@ -198,7 +184,6 @@ type
     pattern*: Regex  ## The regex doing the matching.
                      ## Not nil.
     str*: string  ## The string that was matched against.
-                  ## Not nil.
     pcreMatchBounds: seq[HSlice[cint, cint]] ## First item is the bounds of the match
                                             ## Other items are the captures
                                             ## `a` is inclusive start, `b` is exclusive end
@@ -226,18 +211,6 @@ type
     ## for whatever reason. The message contains the error
     ## code.
 
-runnableExamples:
-  # This MUST be kept in sync with the examples in RegexMatch
-  doAssert "abc".match(re"(\w)").get.captures[0] == "a"
-  doAssert "abc".match(re"(?<letter>\w)").get.captures["letter"] == "a"
-  doAssert "abc".match(re"(\w)\w").get.captures[-1] == "ab"
-
-  doAssert "abc".match(re"(\w)").get.captureBounds[0] == 0 .. 0
-  doAssert 0 in "abc".match(re"(\w)").get.captureBounds == true
-  doAssert "abc".match(re"").get.captureBounds[-1] == 0 .. -1
-  doAssert "abc".match(re"abc").get.captureBounds[-1] == 0 .. 2
-
-
 proc destroyRegex(pattern: Regex) =
   pcre.free_substring(cast[cstring](pattern.pcreObj))
   if pattern.pcreExtra != nil:
@@ -540,18 +513,27 @@ proc matchImpl(str: string, pattern: Regex, start, endpos: int, flags: int): Opt
 proc match*(str: string, pattern: Regex, start = 0, endpos = int.high): Option[RegexMatch] =
   ## Like `find(...)<#find,string,Regex,int>`_, but anchored to the start of the
   ## string.
-  ##
   runnableExamples:
-    doAssert "foo".match(re"f").isSome
+    assert "foo".match(re"f").isSome
-    doAssert "foo".match(re"o").isNone
+    assert "foo".match(re"o").isNone
 
+    assert "abc".match(re"(\w)").get.captures[0] == "a"
+    assert "abc".match(re"(?<letter>\w)").get.captures["letter"] == "a"
+    assert "abc".match(re"(\w)\w").get.captures[-1] == "ab"
+
+    assert "abc".match(re"(\w)").get.captureBounds[0] == 0 .. 0
+    assert 0 in "abc".match(re"(\w)").get.captureBounds
+    assert "abc".match(re"").get.captureBounds[-1] == 0 .. -1
+    assert "abc".match(re"abc").get.captureBounds[-1] == 0 .. 2
   return str.matchImpl(pattern, start, endpos, pcre.ANCHORED)
 
 iterator findIter*(str: string, pattern: Regex, start = 0, endpos = int.high): RegexMatch =
   ## Works the same as `find(...)<#find,string,Regex,int>`_, but finds every
-  ## non-overlapping match. `"2222".find(re"22")` is `"22", "22"`, not
+  ## non-overlapping match:
-  ## `"22", "22", "22"`.
+  runnableExamples:
-  ##
+    import std/sugar
+    assert collect(for a in "2222".findIter(re"22"): a.match) == @["22", "22"]
+     # not @["22", "22", "22"]
   ## Arguments are the same as `find(...)<#find,string,Regex,int>`_
   ##
   ## Variants:
@@ -619,11 +601,10 @@ proc contains*(str: string, pattern: Regex, start = 0, endpos = int.high): bool
   ## Determine if the string contains the given pattern between the end and
   ## start positions:
   ## This function is equivalent to `isSome(str.find(pattern, start, endpos))`.
-  ##
   runnableExamples:
-    doAssert "abc".contains(re"bc")
+    assert "abc".contains(re"bc")
-    doAssert not "abc".contains(re"cd")
+    assert not "abc".contains(re"cd")
-    doAssert not "abc".contains(re"a", start = 1)
+    assert not "abc".contains(re"a", start = 1)
 
   return isSome(str.find(pattern, start, endpos))
 
@@ -635,16 +616,16 @@ proc split*(str: string, pattern: Regex, maxSplit = -1, start = 0): seq[string]
   ##
   runnableExamples:
     # -  If the match is zero-width, then the string is still split:
-    doAssert "123".split(re"") == @["1", "2", "3"]
+    assert "123".split(re"") == @["1", "2", "3"]
 
     # -  If the pattern has a capture in it, it is added after the string
     #    split:
-    doAssert "12".split(re"(\d)") == @["", "1", "", "2", ""]
+    assert "12".split(re"(\d)") == @["", "1", "", "2", ""]
 
     # -  If `maxsplit != -1`, then the string will only be split
     #    `maxsplit - 1` times. This means that there will be `maxsplit`
     #    strings in the output seq.
-    doAssert "1.2.3".split(re"\.", maxsplit = 2) == @["1", "2.3"]
+    assert "1.2.3".split(re"\.", maxsplit = 2) == @["1", "2.3"]
 
   result = @[]
   var lastIdx = start
@@ -747,9 +728,9 @@ proc escapeRe*(str: string): string {.gcsafe.} =
   ##
   ## Escaped char: `\ + * ? [ ^ ] $ ( ) { } = ! < > | : -`
   runnableExamples:
-    doAssert escapeRe("fly+wind") == "fly\\+wind"
+    assert escapeRe("fly+wind") == "fly\\+wind"
-    doAssert escapeRe("!") == "\\!"
+    assert escapeRe("!") == "\\!"
-    doAssert escapeRe("nim*") == "nim\\*"
+    assert escapeRe("nim*") == "nim\\*"
 
   #([\\+*?[^\]$(){}=!<>|:-])
   const SpecialCharMatcher = {'\\', '+', '*', '?', '[', '^', ']', '$', '(',