Fix #269 and rewrite DFAMin (#270)

* add test that demonstrates the issue

* remove incorrect extra-source-files entries

* rewrite DFAMin

* add test for older versions of the code

* improve comments

* fix call of `restrictKeys` for older GHC versions

* Revert "remove incorrect extra-source-files entries"

This reverts commit e0126a8.

* rename tests

* add new tests to extra-source-files

* make use of `fold`

* revert formatter changes

* improve comments, fix typos

* fix typos in tests

* Optimize 'number' by removing already assigned start states

A start state cannot belong to several equivalence classes (they are
disjoint), so we can remove already assigned start states from the
list of start states we want to assign.

* Optimize the construction of new states from old states

Since all old states in an equivalence class are equivalent, we only
need the data from one of them to construct the new state.

* Cosmetics: use OldSNum / NewSNum instead of Int; etc.

* Suggestion: Use a plain filter instead of restrictKeys

* remove `restrictKeys` in favour of filter

* use folds to avoid concat

* add `-XDeriveFunctor` to emulated workflow

---------

Co-authored-by: Andreas Abel <andreas.abel@ifi.lmu.de>

Author: nicuveo

.github/workflows/emulated.yml

@@ -44,7 +44,7 @@ jobs:
           # interpret the forward slashes. You're welcome.
           sed -i "s/getDataDir/\(return \"$(pwd | sed 's/\//\\\//g')\\/data\"\)/g" src/Main.hs
           sed -i "s/version/undefined/g" src/Main.hs
-          ghc -XHaskell2010 -XPatternSynonyms -XFlexibleContexts -XMagicHash -XCPP -XNondecreasingIndentation -XScopedTypeVariables -XTupleSections \
+          ghc -XHaskell2010 -XPatternSynonyms -XFlexibleContexts -XMagicHash -XCPP -XNondecreasingIndentation -XScopedTypeVariables -XTupleSections -XDeriveFunctor \
               -package array -package containers -package directory \
               -isrc src/Main.hs \
               -o alex

alex.cabal

@@ -91,6 +91,8 @@ extra-source-files:
         tests/issue_141.x
         tests/issue_197.x
         tests/issue_262.x
+        tests/issue_269_part1.x
+        tests/issue_269_part2.x
         tests/strict_text_typeclass.x
         tests/posn_typeclass_strict_text.x
         tests/tokens_monadUserState_strict_text.x
@@ -113,6 +115,7 @@ executable alex
   default-language:
     Haskell2010
   default-extensions:
+    DeriveFunctor
     PatternSynonyms
     ScopedTypeVariables
     TupleSections

src/AbsSyn.hs

@@ -123,7 +123,7 @@ data RightContext r
   = NoRightContext
   | RightContextRExp r
   | RightContextCode Code
-  deriving (Eq,Ord)
+  deriving (Eq, Ord, Functor)
 
 instance Show RECtx where
   showsPrec _ (RECtx scs _ r rctx code) =