Merge branch 'develop-remove-parseSExpr'. Close #661.

**Description**

The function `copilot-theorem:Copilot.Theorem.Misc.SExpr.parseSExpr` is
not used anywhere in the implementation. The module is internal and not
exposed to the user, so that function does not have and cannot have any
users.

**Type**

- Bug: unused code included in the implementation.

**Additional context**

None.

**Requester**

- Ivan Perez.

**Method to check presence of bug**

The following search finds mentions of `parseSExpr` in the
implementation, showing only the definition:

```
$ grep -nHre 'parseSExpr' copilot**/src copilot**/tests
copilot-theorem/src/Copilot/Theorem/Misc/SExpr.hs:103:parseSExpr :: String -> Maybe (SExpr String)
copilot-theorem/src/Copilot/Theorem/Misc/SExpr.hs:104:parseSExpr str = case parse parser "" str of
```

**Expected result**

The string should be either empty (the function does not exist) or list
further uses.

The following dockerfile checks that `parseSExpr` is not mentioned
anywhere in the code, after which it prints the message "Success":

```Dockerfile
FROM ubuntu:jammy

RUN apt-get update
RUN apt-get install --yes git

SHELL ["/bin/bash", "-c"]
CMD git clone $REPO \
  && cd $NAME \
  && git checkout $COMMIT \
  && ! grep -nHre '\<parseSExpr\>' --include='*.hs' \
  && echo "Success"
```

Command (substitute variables based on new path after merge):
```
$ docker run -e "REPO=https://github.com/Copilot-Language/copilot" -e "NAME=copilot" -e "COMMIT=<HASH>" -it copilot-verify-661
```

**Solution implemented**

Remove the function `Copilot.Theorem.Misc.SExpr.parseSExpr`, as well as
any auxiliary functions or imports exclusively needed by that function,
if any.

Update Cabal file to remove any dependencies no longer necessary due to
the removal of `parseSExpr` and any auxiliary functions.

**Further notes**

None.

Author: ivanperez-keera

copilot-theorem/CHANGELOG

@@ -1,3 +1,6 @@
+2025-09-07
+        * Remove unused function Copilot.Theorem.Misc.SExpr.parseSExpr. (#661)
+
 2025-07-07
         * Version bump (4.5). (#642)
         * Removed unused pragmas. (#613)

copilot-theorem/copilot-theorem.cabal

@@ -54,7 +54,6 @@ library
                           , libBF                 >= 0.6.2 && < 0.7
                           , mtl                   >= 2.0 && < 2.4
                           , panic                 >= 0.4.0 && < 0.5
-                          , parsec                >= 2.0 && < 3.2
                           , parameterized-utils   >= 2.1.1 && < 2.2
                           , pretty                >= 1.0 && < 1.2
                           , process               >= 1.6 && < 1.7

copilot-theorem/src/Copilot/Theorem/Misc/SExpr.hs

@@ -2,10 +2,9 @@
 {-# LANGUAGE Safe              #-}
 
 -- | A representation for structured expression trees, with support for pretty
--- printing and for parsing.
+-- printing.
 module Copilot.Theorem.Misc.SExpr where
 
-import Text.ParserCombinators.Parsec
 import Text.PrettyPrint.HughesPJ as PP hiding (char, Str)
 
 import Control.Monad
@@ -70,37 +69,3 @@ toDoc shouldIndent printAtom expr = case expr of
         doc $$ indent (toDoc shouldIndent printAtom s)
       | otherwise =
         doc <+> toDoc shouldIndent printAtom s
-
--- | Parser for strings of characters separated by spaces into a structured
--- tree.
---
--- Parentheses are interpreted as grouping elements, that is, defining a
--- 'List', which may be empty.
-parser :: GenParser Char st (SExpr String)
-parser =
-  choice [try unitP, nodeP, leafP]
-
-  where
-    symbol     = oneOf "!#$%&|*+-/:<=>?@^_~."
-    lonelyStr  = many1 (alphaNum <|> symbol)
-
-    unitP      = string "()" >> return unit
-
-    leafP      = atom <$> lonelyStr
-
-    nodeP      = do void $ char '('
-                    spaces
-                    st <- sepBy parser spaces
-                    spaces
-                    void $ char ')'
-                    return $ List st
-
--- | Parser for strings of characters separated by spaces into a structured
--- tree.
---
--- Parentheses are interpreted as grouping elements, that is, defining a
--- 'List', which may be empty.
-parseSExpr :: String -> Maybe (SExpr String)
-parseSExpr str = case parse parser "" str of
-  Left s -> error (show s) -- Nothing
-  Right t -> Just t