Fix regex anchor #69 (#80)

* Always wrap regex pattern in ^(..)

Author: chtenb

CHANGELOG.md

@@ -9,6 +9,7 @@ Breaking changes:
 New features:
 
 Bugfixes:
+- Issue #69: Fix regex parser to always wrap pattern inside `^(..)` (#80 by @chtenb)
 
 Other improvements:
 - Added `purs-tidy` formatter (#76 by @thomashoneyman)

src/Text/Parsing/StringParser/CodePoints.purs

@@ -31,7 +31,7 @@ import Data.Either (Either(..))
 import Data.Enum (fromEnum)
 import Data.Foldable (class Foldable, foldMap, elem, notElem)
 import Data.Maybe (Maybe(..))
-import Data.String.CodePoints (codePointAt, drop, indexOf', length, stripPrefix)
+import Data.String.CodePoints (codePointAt, drop, indexOf', length)
 import Data.String.CodeUnits (singleton)
 import Data.String.Pattern (Pattern(..))
 import Data.String.Regex as Regex
@@ -132,10 +132,7 @@ regex pat =
       matchRegex r
   where
   -- ensure the pattern only matches the current position in the parse
-  pattern =
-    case stripPrefix (Pattern "^") pat of
-      Nothing -> "^" <> pat
-      _ -> pat
+  pattern = "^(" <> pat <> ")"
 
   matchRegex :: Regex.Regex -> Parser String
   matchRegex r = Parser \{ str, pos } -> do

src/Text/Parsing/StringParser/CodeUnits.purs

@@ -127,10 +127,7 @@ regex pat =
       matchRegex r
   where
   -- ensure the pattern only matches the current position in the parse
-  pattern =
-    case SCU.stripPrefix (Pattern "^") pat of
-      Nothing -> "^" <> pat
-      _ -> pat
+  pattern = "^(" <> pat <> ")"
 
   matchRegex :: Regex.Regex -> Parser String
   matchRegex r = Parser \{ str, pos } -> do

test/CodePoints.purs

@@ -99,6 +99,8 @@ testCodePoints = do
   assert $ expectResult (NonEmptyList ('0' :| '1' : '2' : '3' : '4' : Nil)) (many1 anyDigit) "01234/"
   assert $ expectResult (NonEmptyList ('5' :| '6' : '7' : '8' : '9' : Nil)) (many1 anyDigit) "56789:"
   assert $ expectResult "aaaa" (regex "a+") "aaaab"
+  assert $ expectResult "aaaa" (regex "^a+") "aaaab"
+  assert $ parseFail (regex "a|b") "xb"
   assert $ expectResult ("a" : "a" : "a" : Nil) (manyTill (string "a") (string "b")) "aaab"
   assert $ expectResult Nil (manyTill (string "a") (string "b")) "b"
   assert $ expectResult (NonEmptyList ("a" :| "a" : "a" : Nil)) (many1Till (string "a") (string "b")) "aaab"

test/CodeUnits.purs

@@ -99,6 +99,8 @@ testCodeUnits = do
   assert $ expectResult (NonEmptyList ('0' :| '1' : '2' : '3' : '4' : Nil)) (many1 anyDigit) "01234/"
   assert $ expectResult (NonEmptyList ('5' :| '6' : '7' : '8' : '9' : Nil)) (many1 anyDigit) "56789:"
   assert $ expectResult "aaaa" (regex "a+") "aaaab"
+  assert $ expectResult "aaaa" (regex "^a+") "aaaab"
+  assert $ parseFail (regex "a|b") "xb"
   assert $ expectResult ("a" : "a" : "a" : Nil) (manyTill (string "a") (string "b")) "aaab"
   assert $ expectResult Nil (manyTill (string "a") (string "b")) "b"
   assert $ expectResult (NonEmptyList ("a" :| "a" : "a" : Nil)) (many1Till (string "a") (string "b")) "aaab"