parseErrorHuman on try.purescript.org

docs/examples/QuickStart.purs

@@ -4,28 +4,65 @@ import Prelude
 
 import Data.Foldable (fold)
 import Effect (Effect)
-import TryPureScript (h1, h3, p, text, render, code)
-import Parsing (Parser, runParser)
+-- https://github.com/purescript/trypurescript/blob/master/staging/src/TryPureScript.purs
+import TryPureScript (h1, h3, p, text, render, code, indent, Doc)
+import Parsing (Parser, runParser, ParseError(..), Position(..))
+-- import Parsing.String (char, parseErrorHuman)
 import Parsing.String (char)
 import Control.Alt ((<|>))
 import Data.Array (many)
+import Data.Either (Either(..))
+-- import Data.Functor (map)
 
 ayebee :: Parser String Boolean
 ayebee = do
   _ <- char 'a'
   b <- char 'b' <|> char 'B'
   pure (b == 'B')
-    
+
 main :: Effect Unit
 main =
   render $ fold
-    [ h1 $ text "Examples for purescript-parsing Quick Start"
-    
+    [ h1 $ text "Examples for Parsing Quick Start"
+
     , p $ text "Run the " <> (code $ text "ayebee") <> text " parser."
     , h3 $ code (text "runParser \"aB\" ayebee")
-    , h3 $ code $ text $ show $ runParser "aB" ayebee
-    
+    , showResult runParser "aB" ayebee
+
     , p $ text "Run the " <> code (text "ayebee") <> text " parser with the " <> code (text "many") <> text " combinator."
     , h3 $ code (text "runParser \"aBabaB\" (many ayebee)")
-    , h3 $ code $ text $ show $ runParser "aBabaB" (many ayebee)
+    , showResult runParser "aBabaB" (many ayebee)
+
+    , p $ text "Run the " <> code (text "ayebee") <> text " parser on unparsable input."
+    , h3 $ code (text "runParser \"aCaB\" ayebee")
+    , showResult runParser "aCaB" ayebee
     ]
+
+showResult
+  :: forall a. Show a
+  => (String -> Parser String a -> Either ParseError a)
+  -> String
+  -> Parser String a
+  -> Doc
+showResult runner input parser =
+  let
+    result = runner input parser
+  in
+  case result of
+    Right x -> indent $ h3$ code $ text $ show x
+    Left err -> fold $ map (indent <<< h3 <<< code <<< text) $ parseErrorHuman input 40 err
+
+-- for when parseErrorHuman becomes available in TryPureScript
+-- https://pursuit.purescript.org/packages/purescript-parsing/10.1.0/docs/Parsing.String#v:parseErrorHuman
+parseErrorHuman :: String -> Int -> ParseError -> Array String
+parseErrorHuman input contextSize (ParseError msg (Position { line, column, index })) =
+  [ msg <> " at position index:" <> show index
+      <> " (line:"
+      <> show line
+      <> ", column:"
+      <> show column
+      <> ")"
+  , ""
+  , input
+  ]
+