Added expression eval; adjusted birdtrack, added sol combinator.

...for a better error message and better perf

.envrc

@@ -0,0 +1 @@
+use nix

.forgejo/workflows/ci.yml

@@ -0,0 +1,2 @@
+runs-on: self-hosted
+

npins/default.nix

@@ -0,0 +1,146 @@
+/*
+  This file is provided under the MIT licence:
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+  The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+# Generated by npins. Do not modify; will be overwritten regularly
+let
+  data = builtins.fromJSON (builtins.readFile ./sources.json);
+  version = data.version;
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range =
+    first: last: if first > last then [ ] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatMapStrings = f: list: concatStrings (map f list);
+  concatStrings = builtins.concatStringsSep "";
+
+  # If the environment variable NPINS_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  # (Taken from Niv for compatibility)
+  mayOverride =
+    name: path:
+    let
+      envVarName = "NPINS_OVERRIDE_${saneName}";
+      saneName = stringAsChars (c: if (builtins.match "[a-zA-Z0-9]" c) == null then "_" else c) name;
+      ersatz = builtins.getEnv envVarName;
+    in
+    if ersatz == "" then
+      path
+    else
+      # this turns the string into an actual Nix path (for both absolute and
+      # relative paths)
+      builtins.trace "Overriding path of \"${name}\" with \"${ersatz}\" due to set \"${envVarName}\"" (
+        if builtins.substring 0 1 ersatz == "/" then
+          /. + ersatz
+        else
+          /. + builtins.getEnv "PWD" + "/${ersatz}"
+      );
+
+  mkSource =
+    name: spec:
+    assert spec ? type;
+    let
+      path =
+        if spec.type == "Git" then
+          mkGitSource spec
+        else if spec.type == "GitRelease" then
+          mkGitSource spec
+        else if spec.type == "PyPi" then
+          mkPyPiSource spec
+        else if spec.type == "Channel" then
+          mkChannelSource spec
+        else if spec.type == "Tarball" then
+          mkTarballSource spec
+        else
+          builtins.throw "Unknown source type ${spec.type}";
+    in
+    spec // { outPath = mayOverride name path; };
+
+  mkGitSource =
+    {
+      repository,
+      revision,
+      url ? null,
+      submodules,
+      hash,
+      branch ? null,
+      ...
+    }:
+    assert repository ? type;
+    # At the moment, either it is a plain git repository (which has an url), or it is a GitHub/GitLab repository
+    # In the latter case, there we will always be an url to the tarball
+    if url != null && !submodules then
+      builtins.fetchTarball {
+        inherit url;
+        sha256 = hash; # FIXME: check nix version & use SRI hashes
+      }
+    else
+      let
+        url =
+          if repository.type == "Git" then
+            repository.url
+          else if repository.type == "GitHub" then
+            "https://github.com/${repository.owner}/${repository.repo}.git"
+          else if repository.type == "GitLab" then
+            "${repository.server}/${repository.repo_path}.git"
+          else
+            throw "Unrecognized repository type ${repository.type}";
+        urlToName =
+          url: rev:
+          let
+            matched = builtins.match "^.*/([^/]*)(\\.git)?$" url;
+
+            short = builtins.substring 0 7 rev;
+
+            appendShort = if (builtins.match "[a-f0-9]*" rev) != null then "-${short}" else "";
+          in
+          "${if matched == null then "source" else builtins.head matched}${appendShort}";
+        name = urlToName url revision;
+      in
+      builtins.fetchGit {
+        rev = revision;
+        inherit name;
+        # hash = hash;
+        inherit url submodules;
+      };
+
+  mkPyPiSource =
+    { url, hash, ... }:
+    builtins.fetchurl {
+      inherit url;
+      sha256 = hash;
+    };
+
+  mkChannelSource =
+    { url, hash, ... }:
+    builtins.fetchTarball {
+      inherit url;
+      sha256 = hash;
+    };
+
+  mkTarballSource =
+    {
+      url,
+      locked_url ? url,
+      hash,
+      ...
+    }:
+    builtins.fetchTarball {
+      url = locked_url;
+      sha256 = hash;
+    };
+in
+if version == 5 then
+  builtins.mapAttrs mkSource data.pins
+else
+  throw "Unsupported format version ${toString version} in sources.json. Try running `npins upgrade`"

npins/sources.json

@@ -0,0 +1,11 @@
+{
+  "pins": {
+    "nixpkgs": {
+      "type": "Channel",
+      "name": "nixpkgs-unstable",
+      "url": "https://releases.nixos.org/nixpkgs/nixpkgs-25.11pre868532.647e5c14cbd5/nixexprs.tar.xz",
+      "hash": "0i6mgl7pm7y4ydrrll7szmv8hhxb3cyny8x1g1a8sp3g5wl3yd9g"
+    }
+  },
+  "version": 5
+}

shell.nix

@@ -0,0 +1,24 @@
+let
+  sources = import ./npins;
+in
+{
+  pkgs ? import sources.nixpkgs { },
+}:
+
+pkgs.mkShell rec {
+  name = "haddock2";
+
+  packages =
+    with pkgs;
+    [
+      haskell.packages.ghc912.ghc
+      zlib
+    ]
+    ++ map haskell.lib.justStaticExecutables [
+      haskellPackages.cabal-gild
+      haskellPackages.fourmolu
+      cabal-install
+    ];
+
+  env.LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath packages;
+}

src/Lexer.hs

@@ -42,6 +42,7 @@ data Token
   | Escape
   | EmphasisOpen
   | EmphasisClose
+  | Expression
   | Header Level
   | MonospaceOpen
   | MonospaceClose
@@ -82,28 +83,44 @@ lexText = go
     Parsec.optionMaybe Parsec.eof >>= \case
       Just _ -> pure []
       Nothing -> do
-        toks <-
-          choice $
-            Parsec.try
-              <$> [ mathMultiline
-                  , mathInline
-                  , escape -- maths go before escape to avoid mismatch
-                  , headers
-                  , newlineToken
-                  , spaceToken
-                  , link
-                  , labeledLink
-                  , module_
-                  , anchor
-                  , numericEntity
-                  , textElement
-                  , quotes
-                  , birdTrack
-                  , other
-                  ]
+        toks <- topLevel
         rest <- go
         pure (toks <> rest)
 
+{- FOURMOLU_DISABLE -}
+  topLevel =
+    -- backtracking here so we always have a chance to try "other", the "catch-all-leave-to-parser-to-deal-with" choice
+    -- TODO: is this desirable? do we throw lexer error at all?
+    try
+      ( choice
+          -- Sorted in
+          -- - longest to shortest parse path
+          -- - highest frequency to lowest frequency (for performance?)
+          -- - more exact to more freeform (the latter can be the former but not vice versa)
+          [ spaceToken
+          , newlineToken
+
+          , try module_
+          , quotes
+          , try expression
+          , birdTrack
+
+            -- starts with "\"
+          , try mathMultiline
+          , try mathInline
+          , escape
+
+          , headers
+          , labeledLink
+          , link
+          , anchor
+          , numericEntity
+          , textElement
+          ]
+      )
+      <|> other
+{- FOURMOLU_ENABLE -}
+
 -- Tokens
 
 textElement :: Parser [LocatedToken]
@@ -143,16 +160,26 @@ delimited openP closeP openTok closeTok = asList <$> delimitedAsTuple (openTok <
   asList (a, tok, b) = [a, tok, b]
 
 delimitedNoTrailing :: Parser open -> Parser close -> Token -> Parser [LocatedToken]
-delimitedNoTrailing openP closeP openTok = asList <$> delimitedAsTuple (openTok <$ openP) (void closeP)
+delimitedNoTrailing openP closeP openTok =
+  asList <$> delimitedAsTuple (openTok <$ openP) (void closeP)
  where
   asList (a, tok, _) = [a, tok]
 
 delimitedSymmetric :: Parser a -> Token -> Token -> Parser [LocatedToken]
 delimitedSymmetric s = delimited s s
 
+--- End of line // end of file
 eol :: Parser ()
 eol = void "\n" <|> void "\r\n" <|> Parsec.eof
 
+-- Start of line // start of file
+sol :: Parser ()
+sol = do
+  p <- getPosition
+  if sourceColumn p == 1
+    then pure ()
+    else fail "Not at start of line/document"
+
 header1 :: Lexer
 header1 = delimitedNoTrailing "= " eol (Header One)
 
@@ -239,8 +266,15 @@ mathMultiline = delimited "\\[" "\\]" MathMultilineOpen MathMultilineClose
 mathInline :: Lexer
 mathInline = delimited "\\(" "\\)" MathInlineOpen MathInlineClose
 
+-- TODO: make sure this starts at column 0?
 birdTrack :: Lexer
-birdTrack = delimitedNoTrailing ">> " eol BirdTrack
+birdTrack = delimitedNoTrailing (sol <* "> ") eol BirdTrack
+
+-- TODO: also match following lines iff:
+-- they start with alphanum
+-- they're not empty
+expression :: Lexer
+expression = delimitedNoTrailing (sol <* ">>> ") eol Expression
 
 escape :: Lexer
 escape = delimitedNoTrailing "\\" eol Escape

test/Spec.hs

@@ -18,7 +18,7 @@ main = hspec $ do
     describe "minimal" do
       it "handles unicode" unicode
       it "escapes" escaping
-      it "maths" math
+      it "maths" maths
       it "anchors" anchor
       it "space chars" space
       it "bare string" someString
@@ -29,6 +29,7 @@ main = hspec $ do
       it "bird tracks" birdTracks
       it "module names" modules
       it "quotes" quotes
+      it "expressions" expressions
       it "numeric entity" numericEntity
       it "ignores nesting" ignoreNesting
 
@@ -91,8 +92,8 @@ anchor =
     `shouldLexTo` [ (1, 1, Anchor "myAnchor")
                   ]
 
-math :: IO ()
-math = do
+maths :: IO ()
+maths = do
   "\\[some math\\]"
     `shouldLexTo` [ (1, 1, MathMultilineOpen)
                   , (1, 3, Token "some math")
@@ -128,10 +129,35 @@ ignoreNesting =
                   ]
 
 birdTracks :: Expectation
-birdTracks =
-  ">> code"
+birdTracks = do
+  "> code line"
     `shouldLexTo` [ (1, 1, BirdTrack)
-                  , (1, 4, Token "code")
+                  , (1, 3, Token "code line")
+                  ]
+  " > not code"
+    `shouldLexTo` [ (1, 1, Space)
+                  , (1, 2, Token ">")
+                  , (1, 3, Space)
+                  , (1, 4, Token "not")
+                  , (1, 7, Space)
+                  , (1, 8, Token "code")
+                  ]
+
+expressions :: Expectation
+expressions = do
+  ">>> eval this"
+    `shouldLexTo` [ (1, 1, Expression)
+                  , (1, 5, Token "eval this")
+                  ]
+  " >>> not eval this"
+    `shouldLexTo` [ (1, 1, Space)
+                  , (1, 2, Token ">>>")
+                  , (1, 5, Space)
+                  , (1, 6, Token "not")
+                  , (1, 9, Space)
+                  , (1, 10, Token "eval")
+                  , (1, 14, Space)
+                  , (1, 15, Token "this")
                   ]
 
 quotes :: Expectation