From 51fe35c60f5a560c32c5ee26c4317d7858ac7fde Mon Sep 17 00:00:00 2001
From: Philippe Pittoli <karchnu@karchnu.fr>
Date: Tue, 9 Jan 2024 07:24:41 +0100
Subject: [PATCH] Simple generic parsing functions for common searched
 elements.

---
 src/Main.purs   |  4 +++
 src/Parser.purs | 70 +++++++++++++++++++++++++++++--------------------
 2 files changed, 45 insertions(+), 29 deletions(-)

diff --git a/src/Main.purs b/src/Main.purs
index e37aedb..ae48c38 100644
--- a/src/Main.purs
+++ b/src/Main.purs
@@ -47,6 +47,10 @@ main = do
     Just (Tuple x y) -> show x <> " " <> show y
     Nothing -> "failed"
 
+  log $ "parsing 'fic' in 'fiction' (string): " <> case parse (string "fic") "fiction" of
+    Just (Tuple x y) -> show x <> " " <> show y
+    Nothing -> "failed"
+
 -- JUST WORKS
 --  isffound $ parse isf "fable"
 --  isffound $ parse isf "f"
diff --git a/src/Parser.purs b/src/Parser.purs
index 79d96c6..7aaf11a 100644
--- a/src/Parser.purs
+++ b/src/Parser.purs
@@ -5,14 +5,14 @@ import Prelude
 import Data.Array as A
 import Data.Maybe (Maybe(..))
 import Data.Tuple (Tuple(..))
-import Data.String.CodeUnits (uncons, toCharArray, fromCharArray)
+import Data.String.CodeUnits (singleton, uncons, toCharArray, fromCharArray)
 
 newtype Parser v = Parser (String -> Maybe (Tuple v String))
 parse :: forall a. Parser a -> (String -> Maybe (Tuple a String))
 parse (Parser p) = p
 
-itemP :: Parser Char
-itemP = Parser p
+item :: Parser Char
+item = Parser p
   where p str = case uncons str of
                   Nothing -> Nothing
                   Just { head: x, tail: xs } -> Just (Tuple x xs)
@@ -41,35 +41,47 @@ instance bindParser :: Bind Parser where
       let (Parser p2) = f x
       in p2 xs
 
-charP :: Char -> Parser Boolean
-charP c = (_ == c) <$> itemP
-
 -- Next steps.
+empty :: forall a. Parser a
+empty = Parser \_ -> Nothing
+
 sat :: (Char -> Boolean) -> Parser Char
-sat f = Parser p
-  where
-    p stream = case uncons stream of
-      Nothing -> Nothing
-      Just { head: x, tail: xs } -> if f x then Just (Tuple x xs)
-                                           else Nothing
+sat p = do x <- item
+           if p x then pure x else empty
 
-emptyP :: forall a. Parser a
-emptyP = Parser \_ -> Nothing
+isDigit :: Char -> Boolean
+isDigit = between '0' '9'
 
-sat2 :: (Char -> Boolean) -> Parser Char
-sat2 p = do x <- itemP
-            if p x then pure x else emptyP
+digit :: Parser Char
+digit = sat isDigit
 
---try :: Parser a -> Parser a
---try p = Parser p'
---  where
---    p' = case parse p of
---           Nothing -> p
---           Just 
--- orElse, (<|>) :: Parser a -> Parser a -> Parser a
+isLower :: Char -> Boolean
+isLower = between 'a' 'z'
 
-stringP :: String -> Parser Boolean
-stringP str = case A.uncons (toCharArray str) of
-  Nothing -> Parser \stream -> Just (Tuple true stream)
-  Just { head: x, tail: xs } -> do _ <- charP x
-                                   stringP (fromCharArray xs)
+lower :: Parser Char
+lower = sat isLower
+
+isUpper :: Char -> Boolean
+isUpper = between 'A' 'Z'
+
+upper :: Parser Char
+upper = sat isUpper
+
+isAlpha :: Char -> Boolean
+isAlpha c = A.any (\f -> f c) [isLower, isUpper]
+
+letter :: Parser Char
+letter = sat isAlpha
+
+char :: Char -> Parser Char
+char x = sat (_ == x)
+
+concat :: Char -> String -> String
+concat c rest = singleton c <> rest
+
+string :: String -> Parser String
+string str = case A.uncons (toCharArray str) of
+  Nothing -> Parser \stream -> Just (Tuple "" stream)
+  Just { head: x, tail: xs } -> do c <- char x
+                                   rest <- string (fromCharArray xs)
+                                   pure (concat c rest)