# buildLisp provides Nix functions to build Common Lisp packages,
# targeting SBCL.
#
# buildLisp is designed to enforce conventions and do away with the
# free-for-all of existing Lisp build systems.

{ pkgs ? import <nixpkgs> { }, ... }:

let
  inherit (builtins) map elemAt match filter;
  inherit (pkgs) lib runCommand makeWrapper writeText writeShellScriptBin sbcl ecl-static ccl;
  inherit (pkgs.stdenv) targetPlatform;

  #
  # Internal helper definitions
  #

  defaultImplementation = impls.sbcl;

  # Many Common Lisp implementations (like ECL and CCL) will occasionally drop
  # you into an interactive debugger even when executing something as a script.
  # In nix builds we don't want such a situation: Any error should make the
  # script exit non-zero. Luckily the ANSI standard specifies *debugger-hook*
  # which is invoked before the debugger letting us just do that.
  disableDebugger = writeText "disable-debugger.lisp" ''
    (setf *debugger-hook*
          (lambda (error hook)
            (declare (ignore hook))
            (format *error-output* "~%Unhandled error: ~a~%" error)
            #+ccl (quit 1)
            #+ecl (ext:quit 1)))
  '';

  # Process a list of arbitrary values which also contains “implementation
  # filter sets” which describe conditonal inclusion of elements depending
  # on the CL implementation used. Elements are processed in the following
  # manner:
  #
  # * Paths, strings, derivations are left as is
  # * A non-derivation attribute set is processed like this:
  #   1. If it has an attribute equal to impl.name, replace with its value.
  #   2. Alternatively use the value of the "default" attribute.
  #   3. In all other cases delete the element from the list.
  #
  # This can be used to express dependencies or source files which are specific
  # to certain implementations:
  #
  #  srcs = [
  #    # mixable with unconditional entries
  #    ./package.lisp
  #
  #    # implementation specific source files
  #    {
  #      ccl = ./impl-ccl.lisp;
  #      sbcl = ./impl-sbcl.lisp;
  #      ecl = ./impl-ecl.lisp;
  #    }
  #  ];
  #
  #  deps = [
  #    # this dependency is ignored if impl.name != "sbcl"
  #    { sbcl = buildLisp.bundled "sb-posix"; }
  #
  #    # only special casing for a single implementation
  #    {
  #      sbcl = buildLisp.bundled "uiop";
  #      default = buildLisp.bundled "asdf";
  #    }
  #  ];
  implFilter = impl: xs:
    let
      isFilterSet = x: builtins.isAttrs x && !(lib.isDerivation x);
    in
    builtins.map
      (
        x: if isFilterSet x then x.${impl.name} or x.default else x
      )
      (builtins.filter
        (
          x: !(isFilterSet x) || x ? ${impl.name} || x ? default
        )
        xs);

  # Generates lisp code which instructs the given lisp implementation to load
  # all the given dependencies.
  genLoadLispGeneric = impl: deps:
    lib.concatStringsSep "\n"
      (map (lib: "(load \"${lib}/${lib.lispName}.${impl.faslExt}\")")
        (allDeps impl deps));

  # 'genTestLispGeneric' generates a Lisp file that loads all sources and deps
  # and executes expression for a given implementation description.
  genTestLispGeneric = impl: { name, srcs, deps, expression }: writeText "${name}.lisp" ''
    ;; Dependencies
    ${impl.genLoadLisp deps}

    ;; Sources
    ${lib.concatStringsSep "\n" (map (src: "(load \"${src}\")") srcs)}

    ;; Test expression
    (unless ${expression}
      (exit :code 1))
  '';

  # 'dependsOn' determines whether Lisp library 'b' depends on 'a'.
  dependsOn = a: b: builtins.elem a b.lispDeps;

  # 'allDeps' flattens the list of dependencies (and their
  # dependencies) into one ordered list of unique deps which
  # all use the given implementation.
  allDeps = impl: deps:
    let
      # The override _should_ propagate itself recursively, as every derivation
      # would only expose its actually used dependencies. Use implementation
      # attribute created by withExtras if present, override in all other cases
      # (mainly bundled).
      deps' = builtins.map
        (dep: dep."${impl.name}" or (dep.overrideLisp (_: {
          implementation = impl;
        })))
        deps;
    in
    (lib.toposort dependsOn (lib.unique (
      lib.flatten (deps' ++ (map (d: d.lispDeps) deps'))
    ))).result;

  # 'allNative' extracts all native dependencies of a dependency list
  # to ensure that library load paths are set correctly during all
  # compilations and program assembly.
  allNative = native: deps: lib.unique (
    lib.flatten (native ++ (map (d: d.lispNativeDeps) deps))
  );

  # Add an `overrideLisp` attribute to a function result that works
  # similar to `overrideAttrs`, but is used specifically for the
  # arguments passed to Lisp builders.
  makeOverridable = f: orig: (f orig) // {
    overrideLisp = new: makeOverridable f (orig // (new orig));
  };

  # This is a wrapper arround 'makeOverridable' which performs its
  # function, but also adds a the following additional attributes to the
  # resulting derivation, namely a repl attribute which builds a `lispWith`
  # derivation for the current implementation and additional attributes for
  # every all implementations. So `drv.sbcl` would build the derivation
  # with SBCL regardless of what was specified in the initial arguments.
  withExtras = f: args:
    let
      drv = (makeOverridable f) args;
    in
    lib.fix (self:
      drv.overrideLisp
        (old:
          let
            implementation = old.implementation or defaultImplementation;
            brokenOn = old.brokenOn or [ ];
            targets = lib.subtractLists (brokenOn ++ [ implementation.name ])
              (builtins.attrNames impls);
          in
          {
            passthru = (old.passthru or { }) // {
              repl = implementation.lispWith [ self ];

              # meta is done via passthru to minimize rebuilds caused by overriding
              meta = (old.passthru.meta or { }) // {
                ci = (old.passthru.meta.ci or { }) // {
                  inherit targets;
                };
              };
            } // builtins.listToAttrs (builtins.map
              (impl: {
                inherit (impl) name;
                value = self.overrideLisp (_: {
                  implementation = impl;
                });
              })
              (builtins.attrValues impls));
          }) // {
        overrideLisp = new: withExtras f (args // new args);
      });

  # 'testSuite' builds a Common Lisp test suite that loads all of srcs and deps,
  # and then executes expression to check its result
  testSuite = { name, expression, srcs, deps ? [ ], native ? [ ], implementation }:
    let
      lispDeps = allDeps implementation (implFilter implementation deps);
      lispNativeDeps = allNative native lispDeps;
      filteredSrcs = implFilter implementation srcs;
    in
    runCommand name
      {
        LD_LIBRARY_PATH = lib.makeLibraryPath lispNativeDeps;
        LANG = "C.UTF-8";
      } ''
      echo "Running test suite ${name}"

      ${implementation.runScript} ${
        implementation.genTestLisp {
          inherit name expression;
          srcs = filteredSrcs;
          deps = lispDeps;
        }
      } | tee $out

      echo "Test suite ${name} succeeded"
    '';

  # 'impls' is an attribute set of attribute sets which describe how to do common
  # tasks when building for different Common Lisp implementations. Each
  # implementation set has the following members:
  #
  # Required members:
  #
  # - runScript :: string
  #   Describes how to invoke the implementation from the shell, so it runs a
  #   lisp file as a script and exits.
  # - faslExt :: string
  #   File extension of the implementations loadable (FASL) files.
  #   Implementations are free to generate native object files, but with the way
  #   buildLisp works it is required that we can also 'load' libraries, so
  #   (additionally) building a FASL or equivalent is required.
  # - genLoadLisp :: [ dependency ] -> string
  #   Returns lisp code to 'load' the given dependencies. 'genLoadLispGeneric'
  #   should work for most dependencies.
  # - genCompileLisp :: { name, srcs, deps } -> file
  #   Builds a lisp file which instructs the implementation to build a library
  #   from the given source files when executed. After running at least
  #   the file "$out/${name}.${impls.${implementation}.faslExt}" should have
  #   been created.
  # - genDumpLisp :: { name, main, deps } -> file
  #   Builds a lisp file which instructs the implementation to build an
  #   executable which runs 'main' (and exits) where 'main' is available from
  #   'deps'. The executable should be created as "$out/bin/${name}", usually
  #   by dumping the lisp image with the replaced toplevel function replaced.
  # - wrapProgram :: boolean
  #   Whether to wrap the resulting binary / image with a wrapper script setting
  #   `LD_LIBRARY_PATH`.
  # - genTestLisp :: { name, srcs, deps, expression } -> file
  #   Builds a lisp file which loads the given 'deps' and 'srcs' files and
  #   then evaluates 'expression'. Depending on whether 'expression' returns
  #   true or false, the script must exit with a zero or non-zero exit code.
  #   'genTestLispGeneric' will work for most implementations.
  # - lispWith :: [ dependency ] -> drv
  #   Builds a script (or dumped image) which when executed loads (or has
  #   loaded) all given dependencies. When built this should create an executable
  #   at "$out/bin/${implementation}".
  #
  # Optional members:
  #
  # - bundled :: string -> library
  #   Allows giving an implementation specific builder for a bundled library.
  #   This function is used as a replacement for the internal defaultBundled
  #   function and only needs to support one implementation. The returned derivation
  #   must behave like one built by 'library' (in particular have the same files
  #   available in "$out" and the same 'passthru' attributes), but may be built
  #   completely differently.
  impls = lib.mapAttrs (name: v: { inherit name; } // v) {
    sbcl = {
      runScript = "${sbcl}/bin/sbcl --script";
      faslExt = "fasl";

      # 'genLoadLisp' generates Lisp code that instructs SBCL to load all
      # the provided Lisp libraries.
      genLoadLisp = genLoadLispGeneric impls.sbcl;

      # 'genCompileLisp' generates a Lisp file that instructs SBCL to
      # compile the provided list of Lisp source files to "$out/${name}.fasl".
      genCompileLisp = { name, srcs, deps }: writeText "sbcl-compile.lisp" ''
        ;; This file compiles the specified sources into the Nix build
        ;; directory, creating one FASL file for each source.
        (require 'sb-posix)

        ${impls.sbcl.genLoadLisp deps}

        (defun nix-compile-lisp (srcfile)
          (let ((outfile (make-pathname :type "fasl"
                                        :directory (or (sb-posix:getenv "NIX_BUILD_TOP")
                                                       (error "not running in a Nix build"))
                                        :name (substitute #\- #\/ srcfile))))
            (multiple-value-bind (out-truename _warnings-p failure-p)
                (compile-file srcfile :output-file outfile)
              (if failure-p (sb-posix:exit 1)
                  (progn
                    ;; For the case of multiple files belonging to the same
                    ;; library being compiled, load them in order:
                    (load out-truename)

                    ;; Return pathname as a string for cat-ting it later
                    (namestring out-truename))))))

        (let ((*compile-verbose* t)
              (catted-fasl (make-pathname :type "fasl"
                                          :directory (or (sb-posix:getenv "out")
                                                         (error "not running in a Nix build"))
                                          :name "${name}")))

          (with-open-file (file catted-fasl
                                :direction :output
                                :if-does-not-exist :create)

            ;; SBCL's FASL files can just be bundled together using cat
            (sb-ext:run-program "cat"
             (mapcar #'nix-compile-lisp
              ;; These forms were inserted by the Nix build:
              '(${
                lib.concatMapStringsSep "\n" (src: "\"${src}\"") srcs
              }))
             :output file :search t)))
      '';

      # 'genDumpLisp' generates a Lisp file that instructs SBCL to dump
      # the currently loaded image as an executable to $out/bin/$name.
      #
      # TODO(tazjin): Compression is currently unsupported because the
      # SBCL in nixpkgs is, by default, not compiled with zlib support.
      genDumpLisp = { name, main, deps }: writeText "sbcl-dump.lisp" ''
        (require 'sb-posix)

        ${impls.sbcl.genLoadLisp deps}

        (let* ((bindir (concatenate 'string (sb-posix:getenv "out") "/bin"))
               (outpath (make-pathname :name "${name}"
                                       :directory bindir)))

          ;; Tell UIOP that argv[0] will refer to running image, not the lisp impl
          (when (find-package :uiop)
            (eval `(setq ,(find-symbol "*IMAGE-DUMPED-P*" :uiop) :executable)))

          (save-lisp-and-die outpath
                             :executable t
                             :toplevel
                             (lambda ()
                               ;; Filter out everything prior to the `--` we
                               ;; insert in the wrapper to prevent SBCL from
                               ;; parsing arguments at startup
                               (setf sb-ext:*posix-argv*
                                     (delete "--" sb-ext:*posix-argv*
                                             :test #'string= :count 1))
                               (${main}))
                             :purify t))
      '';

      wrapProgram = true;

      genTestLisp = genTestLispGeneric impls.sbcl;

      lispWith = deps:
        let lispDeps = filter (d: !d.lispBinary) (allDeps impls.sbcl deps);
        in writeShellScriptBin "sbcl" ''
          export LD_LIBRARY_PATH="${lib.makeLibraryPath (allNative [] lispDeps)}"
          export LANG="C.UTF-8"
          exec ${sbcl}/bin/sbcl ${
            lib.optionalString (deps != [])
              "--load ${writeText "load.lisp" (impls.sbcl.genLoadLisp lispDeps)}"
          } $@
        '';
    };
    ecl = {
      runScript = "${ecl-static}/bin/ecl --load ${disableDebugger} --shell";
      faslExt = "fasc";
      genLoadLisp = genLoadLispGeneric impls.ecl;
      genCompileLisp = { name, srcs, deps }: writeText "ecl-compile.lisp" ''
        ;; This seems to be required to bring make the 'c' package available
        ;; early, otherwise ECL tends to fail with a read failure…
        (ext:install-c-compiler)

        ;; Load dependencies
        ${impls.ecl.genLoadLisp deps}

        (defun getenv-or-fail (var)
          (or (ext:getenv var)
              (error (format nil "Missing expected environment variable ~A" var))))

        (defun nix-compile-file (srcfile &key native)
          "Compile the given srcfile into a compilation unit in :out-dir using
          a unique name based on srcfile as the filename which is returned after
          compilation. If :native is true, create an native object file,
          otherwise a byte-compile fasc file is built and immediately loaded."

          (let* ((unique-name (substitute #\_ #\/ srcfile))
                 (out-file (make-pathname :type (if native "o" "fasc")
                                          :directory (getenv-or-fail "NIX_BUILD_TOP")
                                          :name unique-name)))
            (multiple-value-bind (out-truename _warnings-p failure-p)
                (compile-file srcfile :system-p native
                                      :load (not native)
                                      :output-file out-file
                                      :verbose t :print t)
              (if failure-p (ext:quit 1) out-truename))))

        (let* ((out-dir (getenv-or-fail "out"))
               (nix-build-dir (getenv-or-fail "NIX_BUILD_TOP"))
               (srcs
                ;; These forms are inserted by the Nix build
                '(${lib.concatMapStringsSep "\n" (src: "\"${src}\"") srcs})))

          ;; First, we'll byte compile loadable FASL files and load them
          ;; immediately. Since we are using a statically linked ECL, there's
          ;; no way to load native objects, so we rely on byte compilation
          ;; for all our loading — which is crucial in compilation of course.
          (ext:install-bytecodes-compiler)

          ;; ECL's bytecode FASLs can just be concatenated to create a bundle
          ;; at least since a recent bugfix which we apply as a patch.
          ;; See also: https://gitlab.com/embeddable-common-lisp/ecl/-/issues/649
          (let ((bundle-out (make-pathname :type "fasc" :name "${name}"
                                           :directory out-dir)))

            (with-open-file (fasc-stream bundle-out :direction :output)
              (ext:run-program "cat"
                               (mapcar (lambda (f)
                                         (namestring
                                          (nix-compile-file f :native nil)))
                                       srcs)
                               :output fasc-stream)))

          (ext:install-c-compiler)

          ;; Build a (natively compiled) static archive (.a) file. We want to
          ;; use this for (statically) linking an executable later. The bytecode
          ;; dance is only required because we can't load such archives.
          (c:build-static-library
           (make-pathname :type "a" :name "${name}" :directory out-dir)
           :lisp-files (mapcar (lambda (x)
                                 (nix-compile-file x :native t))
                               srcs)))
      '';
      genDumpLisp = { name, main, deps }: writeText "ecl-dump.lisp" ''
        (defun getenv-or-fail (var)
          (or (ext:getenv var)
              (error (format nil "Missing expected environment variable ~A" var))))

        ${impls.ecl.genLoadLisp deps}

        ;; makes a 'c' package available that can link executables
        (ext:install-c-compiler)

        (c:build-program
         (merge-pathnames (make-pathname :directory '(:relative "bin")
                                         :name "${name}")
                          (truename (getenv-or-fail "out")))
         :epilogue-code `(progn
                          ;; UIOP doesn't understand ECL, so we need to make it
                          ;; aware that we are a proper executable, causing it
                          ;; to handle argument parsing and such properly. Since
                          ;; this needs to work even when we're not using UIOP,
                          ;; we need to do some compile-time acrobatics.
                          ,(when (find-package :uiop)
                            `(setf ,(find-symbol "*IMAGE-DUMPED-P*" :uiop) :executable))
                          ;; Run the actual application…
                          (${main})
                          ;; … and exit.
                          (ext:quit))
         ;; ECL can't remember these from its own build…
         :ld-flags '("-static")
         :lisp-files
         ;; The following forms are inserted by the Nix build
         '(${
             lib.concatMapStrings (dep: ''
               "${dep}/${dep.lispName}.a"
             '') (allDeps impls.ecl deps)
           }))
      '';

      wrapProgram = false;

      genTestLisp = genTestLispGeneric impls.ecl;

      lispWith = deps:
        let lispDeps = filter (d: !d.lispBinary) (allDeps impls.ecl deps);
        in writeShellScriptBin "ecl" ''
          exec ${ecl-static}/bin/ecl ${
            lib.optionalString (deps != [])
              "--load ${writeText "load.lisp" (impls.ecl.genLoadLisp lispDeps)}"
          } $@
        '';

      bundled = name: runCommand "${name}-cllib"
        {
          passthru = {
            lispName = name;
            lispNativeDeps = [ ];
            lispDeps = [ ];
            lispBinary = false;
            repl = impls.ecl.lispWith [ (impls.ecl.bundled name) ];
          };
        } ''
        mkdir -p "$out"
        ln -s "${ecl-static}/lib/ecl-${ecl-static.version}/${name}.${impls.ecl.faslExt}" -t "$out"
        ln -s "${ecl-static}/lib/ecl-${ecl-static.version}/lib${name}.a" "$out/${name}.a"
      '';
    };
    ccl = {
      # Relatively bespoke wrapper script necessary to make CCL just™ execute
      # a lisp file as a script.
      runScript = pkgs.writers.writeBash "ccl" ''
        # don't print intro message etc.
        args=("--quiet")

        # makes CCL crash on error instead of entering the debugger
        args+=("--load" "${disableDebugger}")

        # load files from command line in order
        for f in "$@"; do
          args+=("--load" "$f")
        done

        # Exit if everything was processed successfully
        args+=("--eval" "(quit)")

        exec ${ccl}/bin/ccl ''${args[@]}
      '';

      # See https://ccl.clozure.com/docs/ccl.html#building-definitions
      faslExt =
        /**/
        if targetPlatform.isPowerPC && targetPlatform.is32bit then "pfsl"
        else if targetPlatform.isPowerPC && targetPlatform.is64bit then "p64fsl"
        else if targetPlatform.isx86_64 && targetPlatform.isLinux then "lx64fsl"
        else if targetPlatform.isx86_32 && targetPlatform.isLinux then "lx32fsl"
        else if targetPlatform.isAarch32 && targetPlatform.isLinux then "lafsl"
        else if targetPlatform.isx86_32 && targetPlatform.isDarwin then "dx32fsl"
        else if targetPlatform.isx86_64 && targetPlatform.isDarwin then "dx64fsl"
        else if targetPlatform.isx86_64 && targetPlatform.isDarwin then "dx64fsl"
        else if targetPlatform.isx86_32 && targetPlatform.isFreeBSD then "fx32fsl"
        else if targetPlatform.isx86_64 && targetPlatform.isFreeBSD then "fx64fsl"
        else if targetPlatform.isx86_32 && targetPlatform.isWindows then "wx32fsl"
        else if targetPlatform.isx86_64 && targetPlatform.isWindows then "wx64fsl"
        else builtins.throw "Don't know what FASLs are called for this platform: "
          + pkgs.stdenv.targetPlatform.system;

      genLoadLisp = genLoadLispGeneric impls.ccl;

      genCompileLisp = { name, srcs, deps }: writeText "ccl-compile.lisp" ''
        ${impls.ccl.genLoadLisp deps}

        (defun getenv-or-fail (var)
          (or (getenv var)
              (error (format nil "Missing expected environment variable ~A" var))))

        (defun nix-compile-file (srcfile)
          "Trivial wrapper around COMPILE-FILE which causes CCL to exit if
          compilation fails and LOADs the compiled file on success."
          (let ((output (make-pathname :name (substitute #\_ #\/ srcfile)
                                       :type "${impls.ccl.faslExt}"
                                       :directory (getenv-or-fail "NIX_BUILD_TOP"))))
            (multiple-value-bind (out-truename _warnings-p failure-p)
                (compile-file srcfile :output-file output :print t :verbose t)
                (declare (ignore _warnings-p))
              (if failure-p (quit 1)
                  (progn (load out-truename) out-truename)))))

        (fasl-concatenate (make-pathname :name "${name}" :type "${impls.ccl.faslExt}"
                                         :directory (getenv-or-fail "out"))
                          (mapcar #'nix-compile-file
                                  ;; These forms where inserted by the Nix build
                                  '(${
                                      lib.concatMapStrings (src: ''
                                        "${src}"
                                      '') srcs
                                   })))
      '';

      genDumpLisp = { name, main, deps }: writeText "ccl-dump.lisp" ''
        ${impls.ccl.genLoadLisp deps}

        (let* ((out (or (getenv "out") (error "Not running in a Nix build")))
               (bindir (concatenate 'string out "/bin/"))
               (executable (make-pathname :directory bindir :name "${name}")))

          ;; Tell UIOP that argv[0] will refer to running image, not the lisp impl
          (when (find-package :uiop)
            (eval `(setf ,(find-symbol "*IMAGE-DUMPED-P*" :uiop) :executable)))

          (save-application executable
                            :purify t
                            :error-handler :quit
                            :toplevel-function
                            (lambda ()
                              ;; Filter out everything prior to the `--` we
                              ;; insert in the wrapper to prevent SBCL from
                              ;; parsing arguments at startup
                              (setf ccl:*command-line-argument-list*
                                    (delete "--" ccl:*command-line-argument-list*
                                                 :test #'string= :count 1))
                              (${main}))
                            :mode #o755
                            ;; TODO(sterni): use :native t on macOS
                            :prepend-kernel t))
      '';

      wrapProgram = true;

      genTestLisp = genTestLispGeneric impls.ccl;

      lispWith = deps:
        let lispDeps = filter (d: !d.lispBinary) (allDeps impls.ccl deps);
        in writeShellScriptBin "ccl" ''
          export LD_LIBRARY_PATH="${lib.makeLibraryPath (allNative [] lispDeps)}"
          exec ${ccl}/bin/ccl ${
            lib.optionalString (deps != [])
              "--load ${writeText "load.lisp" (impls.ccl.genLoadLisp lispDeps)}"
          } "$@"
        '';
    };
  };

  #
  # Public API functions
  #

  # 'library' builds a list of Common Lisp files into an implementation
  # specific library format, usually a single FASL file, which can then be
  # loaded and built into an executable via 'program'.
  library =
    { name
    , implementation ? defaultImplementation
    , brokenOn ? [ ] # TODO(sterni): make this a warning
    , srcs
    , deps ? [ ]
    , native ? [ ]
    , tests ? null
    , passthru ? { }
    }:
    let
      filteredDeps = implFilter implementation deps;
      filteredSrcs = implFilter implementation srcs;
      lispNativeDeps = (allNative native filteredDeps);
      lispDeps = allDeps implementation filteredDeps;
      testDrv =
        if ! isNull tests
        then
          testSuite
            {
              name = tests.name or "${name}-test";
              srcs = filteredSrcs ++ (tests.srcs or [ ]);
              deps = filteredDeps ++ (tests.deps or [ ]);
              expression = tests.expression;
              inherit implementation;
            }
        else null;
    in
    lib.fix (self: runCommand "${name}-cllib"
      {
        LD_LIBRARY_PATH = lib.makeLibraryPath lispNativeDeps;
        LANG = "C.UTF-8";
        passthru = passthru // {
          inherit lispNativeDeps lispDeps;
          lispName = name;
          lispBinary = false;
          tests = testDrv;
        };
      } ''
      ${if ! isNull testDrv
        then "echo 'Test ${testDrv} succeeded'"
        else "echo 'No tests run'"}

      mkdir $out

      ${implementation.runScript} ${
        implementation.genCompileLisp {
          srcs = filteredSrcs;
          inherit name;
          deps = lispDeps;
        }
      }
    '');

  # 'program' creates an executable, usually containing a dumped image of the
  # specified sources and dependencies.
  program =
    { name
    , implementation ? defaultImplementation
    , brokenOn ? [ ] # TODO(sterni): make this a warning
    , main ? "${name}:main"
    , srcs
    , deps ? [ ]
    , native ? [ ]
    , tests ? null
    , passthru ? { }
    }:
    let
      filteredSrcs = implFilter implementation srcs;
      filteredDeps = implFilter implementation deps;
      lispDeps = allDeps implementation filteredDeps;
      libPath = lib.makeLibraryPath (allNative native lispDeps);
      # overriding is used internally to propagate the implementation to use
      selfLib = (makeOverridable library) {
        inherit name native brokenOn;
        deps = lispDeps;
        srcs = filteredSrcs;
      };
      testDrv =
        if ! isNull tests
        then
          testSuite
            {
              name = tests.name or "${name}-test";
              srcs =
                (
                  # testSuite does run implFilter as well
                  filteredSrcs ++ (tests.srcs or [ ])
                );
              deps = filteredDeps ++ (tests.deps or [ ]);
              expression = tests.expression;
              inherit implementation;
            }
        else null;
    in
    lib.fix (self: runCommand "${name}"
      {
        nativeBuildInputs = [ makeWrapper ];
        LD_LIBRARY_PATH = libPath;
        LANG = "C.UTF-8";
        passthru = passthru // {
          lispName = name;
          lispDeps = [ selfLib ];
          lispNativeDeps = native;
          lispBinary = true;
          tests = testDrv;
        };
      }
      (''
        ${if ! isNull testDrv
          then "echo 'Test ${testDrv} succeeded'"
          else ""}
        mkdir -p $out/bin

        ${implementation.runScript} ${
          implementation.genDumpLisp {
            inherit name main;
            deps = ([ selfLib ] ++ lispDeps);
          }
        }
      '' + lib.optionalString implementation.wrapProgram ''
        wrapProgram $out/bin/${name} \
          --prefix LD_LIBRARY_PATH : "${libPath}" \
          --add-flags "\$NIX_BUILDLISP_LISP_ARGS --"
      ''));

  # 'bundled' creates a "library" which makes a built-in package available,
  # such as any of SBCL's sb-* packages or ASDF. By default this is done
  # by calling 'require', but implementations are free to provide their
  # own specific bundled function.
  bundled = name:
    let
      # TODO(sterni): allow overriding args to underlying 'library' (e. g. srcs)
      defaultBundled = implementation: name: library {
        inherit name implementation;
        srcs = lib.singleton (builtins.toFile "${name}.lisp" "(require '${name})");
      };

      bundled' =
        { implementation ? defaultImplementation
        , name
        }:
        implementation.bundled or (defaultBundled implementation) name;

    in
    (makeOverridable bundled') {
      inherit name;
    };

in
{
  library = withExtras library;
  program = withExtras program;
  inherit bundled;

  # 'sbclWith' creates an image with the specified libraries /
  # programs loaded in SBCL.
  sbclWith = impls.sbcl.lispWith;

  inherit (impls)
    sbcl
    ecl
    ccl
    ;
}