From a4f6cdc0781c39b2c12ab787d8cecaf9b8a1c605 Mon Sep 17 00:00:00 2001
From: Jan Sucan <jan@jansucan.com>
Date: Tue, 15 Aug 2023 17:40:13 +0200
Subject: 8_c_1: Add solution

---
 ch08/8_c_1.hs | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 ch08/8_c_1.hs

(limited to 'ch08')

diff --git a/ch08/8_c_1.hs b/ch08/8_c_1.hs
new file mode 100644
index 0000000..ce80ade
--- /dev/null
+++ b/ch08/8_c_1.hs
@@ -0,0 +1,79 @@
+-- Write a version of globToRegex that uses the type signature earlier.
+
+{-- From examples/examples/ch08/GlobRegex.hs modified according to the assignment --}
+import Text.Regex.Posix ((=~))
+
+type GlobError = String
+
+globToRegex :: String -> Either GlobError String
+
+globToRegex cs = propagateError regex
+  where regex = globToRegex' cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right ('^' : s ++ "$")
+
+globToRegex' :: String -> Either GlobError String
+globToRegex' "" = Right ""
+
+globToRegex' ('*':cs) = propagateError regex
+  where regex = globToRegex' cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right (".*" ++ s)
+
+globToRegex' ('?':cs) = propagateError regex
+  where regex = globToRegex' cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right ("." ++ s)
+
+globToRegex' ('[':'!':c:cs) = propagateError charCls
+  where charCls = charClass cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right ("[^" ++ c : s)
+
+globToRegex' ('[':c:cs) = propagateError charCls
+  where charCls = charClass cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right ('['  :  c : s)
+
+globToRegex' ('[':_) = Left "unterminated character class"
+
+globToRegex' (c:cs) = propagateError regex
+  where regex = globToRegex' cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right ((escape c) ++ s)
+
+
+escape :: Char -> String
+escape c | c `elem` regexChars = '\\' : [c]
+         | otherwise = [c]
+    where regexChars = "\\+()^$.{}]|"
+
+
+charClass :: String -> Either GlobError String
+
+charClass (']':cs) = propagateError regex
+  where regex = globToRegex' cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right (']' : s)
+
+charClass (c:cs) = propagateError charCls
+  where charCls = charClass cs
+        propagateError (Left e) = Left e
+        propagateError (Right s) = Right (c : s)
+
+charClass [] = Left "unterminated character class"
+{-- End of code from examples --}
+
+
+-- ghci> :l 8_c_1.hs
+-- [1 of 1] Compiling Main             ( 8_c_1.hs, interpreted )
+-- Ok, one module loaded.
+
+-- ghci> globToRegex "["
+-- Left "unterminated character class"
+
+-- ghci> globToRegex "[]"
+-- Left "unterminated character class"
+
+-- ghci> globToRegex "a?b*c[!DE][FG]+"
+-- Right "^a.b.*c[^DE][FG]\\+$"
-- 
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