From 71786a494c470b855c74a281ac445e135f41b151 Mon Sep 17 00:00:00 2001
From: Humza Shahid <humzasaur@gmail.com>
Date: Mon, 6 Oct 2025 21:58:50 +0100
Subject: [PATCH] fix minor bug with escape sequences: we should pattern match
 on an unescaped char, and we should return an escaped char. For example, it
 makes sense to pattern match on plain unescaped
 /home/humza/Downloads/sml/shf/temp.txt"n" and return
 /home/humza/Downloads/sml/shf/temp.txt"\n". This is because user inputs
 escape-chars as a two-char sequence, prepended by a backslash \ character

---
 fcore/search-list/dfa-gen.sml | 49 ++++++++++++++++++-----------------
 temp.txt                      |  2 +-
 2 files changed, 26 insertions(+), 25 deletions(-)

diff --git a/fcore/search-list/dfa-gen.sml b/fcore/search-list/dfa-gen.sml
index 1ba181c..29e5d7b 100644
--- a/fcore/search-list/dfa-gen.sml
+++ b/fcore/search-list/dfa-gen.sml
@@ -113,25 +113,25 @@ struct
     fun isValidEscapeSequence chr =
       case chr of
       (* regex metacharacters *)
-        #"(" => true
-      | #")" => true
-      | #"[" => true
-      | #"]" => true
-      | #"+" => true
-      | #"*" => true
-      | #"|" => true
-      | #"?" => true
+        #"(" => (true, chr)
+      | #")" => (true, chr)
+      | #"[" => (true, chr)
+      | #"]" => (true, chr)
+      | #"+" => (true, chr)
+      | #"*" => (true, chr)
+      | #"|" => (true, chr)
+      | #"?" => (true, chr)
       (* standard escape sequences *)
-      | #"\a" => true
-      | #"\b" => true
-      | #"\t" => true
-      | #"\n" => true
-      | #"\v" => true
-      | #"\f" => true
-      | #"\r" => true
-      | #"\\" => true
-      | #"\"" => true
-      | _ => false
+      | #"a" => (true, #"\a")
+      | #"b" => (true, #"\b")
+      | #"t" => (true, #"\t")
+      | #"n" => (true, #"\n")
+      | #"v" => (true, #"\v")
+      | #"f" => (true, #"\f")
+      | #"r" => (true, #"\r")
+      | #"\\" => (true, chr)
+      | #"\"" => (true, chr)
+      | _ => (false, chr)
 
     fun computeAtom (pos, str, stateNum) =
       if pos = String.size str then
@@ -151,11 +151,6 @@ struct
                    | NONE => NONE
                  end
              | NONE => NONE)
-        | #")" => NONE
-        | #"?" => NONE
-        | #"*" => NONE
-        | #"+" => NONE
-        | #"." => SOME (pos + 1, WILDCARD (stateNum + 1), stateNum + 1)
         | #"\\" =>
             (* escape sequences *)
             if pos + 1 = String.size str then
@@ -163,8 +158,9 @@ struct
             else
               let
                 val chr = String.sub (str, pos + 1)
+                val (isValid, chr) = isValidEscapeSequence chr
               in
-                if isValidEscapeSequence chr then
+                if isValid then
                   let
                     val chr = CHAR_LITERAL {char = chr, position = stateNum + 1}
                   in
@@ -173,6 +169,11 @@ struct
                 else
                   NONE
               end
+        | #"." => SOME (pos + 1, WILDCARD (stateNum + 1), stateNum + 1)
+        | #")" => NONE
+        | #"?" => NONE
+        | #"*" => NONE
+        | #"+" => NONE
         (* todo: [character classes] *)
         | chr =>
             let val chr = CHAR_LITERAL {char = chr, position = stateNum + 1}
diff --git a/temp.txt b/temp.txt
index cba94ed..c550179 100644
--- a/temp.txt
+++ b/temp.txt
@@ -1,3 +1,3 @@
-hello
+hello(
 fellow
 yellow