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diff --git a/libbuild2/recipe.hxx b/libbuild2/recipe.hxx
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+++ b/libbuild2/recipe.hxx
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+// file      : libbuild2/recipe.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef LIBBUILD2_RECIPE_HXX
+#define LIBBUILD2_RECIPE_HXX
+
+#include <libbuild2/types.hxx>
+#include <libbuild2/forward.hxx>
+#include <libbuild2/utility.hxx>
+
+#include <libbuild2/action.hxx>
+#include <libbuild2/target-state.hxx>
+
+#include <libbuild2/export.hxx>
+
+namespace build2
+{
+  // The returned target state is normally changed or unchanged. If there is
+  // an error, then the recipe should throw failed rather than returning (this
+  // is the only exception that a recipe can throw).
+  //
+  // The return value of the recipe is used to update the target state. If it
+  // is target_state::group then the target's state is the group's state.
+  //
+  // The recipe may also return postponed in which case the target state is
+  // assumed to be unchanged (normally this means a prerequisite was postponed
+  // and while the prerequisite will be re-examined via another dependency,
+  // this target is done).
+  //
+  // Note that max size for the "small capture optimization" in std::function
+  // ranges (in pointer sizes) from 0 (GCC prior to 5) to 2 (GCC 5) to 6 (VC
+  // 14.2). With the size ranging (in bytes for 64-bit target) from 32 (GCC)
+  // to 64 (VC).
+  //
+  using recipe_function = target_state (action, const target&);
+  using recipe = function<recipe_function>;
+
+  // Commonly-used recipes.
+  //
+  // The default recipe executes the action on all the prerequisites in a
+  // loop, skipping ignored. Specifically, for actions with the "first"
+  // execution mode, it calls execute_prerequisites() while for those with
+  // "last" -- reverse_execute_prerequisites() (see <libbuild2/operation.hxx>,
+  // <libbuild2/algorithm.hxx> for details). The group recipe calls the
+  // group's recipe.
+  //
+  LIBBUILD2_SYMEXPORT extern const recipe empty_recipe;
+  LIBBUILD2_SYMEXPORT extern const recipe noop_recipe;
+  LIBBUILD2_SYMEXPORT extern const recipe default_recipe;
+  LIBBUILD2_SYMEXPORT extern const recipe group_recipe;
+}
+
+#endif // LIBBUILD2_RECIPE_HXX