diff --git a/src/instructions.cr b/src/instructions.cr
index 93a7c6c..cf8b509 100644
--- a/src/instructions.cr
+++ b/src/instructions.cr
@@ -1,7 +1,57 @@
 
 class Package::Instructions
+	enum Status
+		Success
+		Failed
+		Pass
+	end
+
+	class BuildDefault
+		getter name : String
+		getter callback : Proc(Recipe, Status)
+		def initialize(@name, &block : Proc(Recipe, Status))
+			@callback = block
+		end
+	end
+
 	class Set < Array(String)
+		def initialize(@defaults_if_empty = Array(BuildDefault).new)
+			super()
+		end
 		# FIXME: def execute
+
+		def run(recipe : Recipe) : Instructions::Status
+			if size > 0
+				# FIXME: Maybe do that for [1] and the others, no?
+				child = Process.run "sh", ["-c", self[0]], output: Process::Redirect::Inherit, error: Process::Redirect::Inherit
+
+				if child.exit_status == 0
+					return Instructions::Status::Success
+				else
+					return Instructions::Status::Failed
+				end
+			end
+
+			@defaults_if_empty.each do |default|
+				rvalue = default.callback.call recipe
+
+				if rvalue == Status::Pass
+					next
+				end
+
+				return rvalue
+			end
+
+			Status::Pass
+		rescue e
+			# Possible TODO: print the origin of the exception (backend, user-provided code, other/unknown).
+			STDERR << "Exception caught: " << e.message << "\n"
+			Status::Failed
+		end
+
+		def <<(other : BuildDefault)
+			@defaults_if_empty << other
+		end
 	end
 
 	getter configure = Set.new
@@ -9,10 +59,41 @@ class Package::Instructions
 	getter install = Set.new
 
 	def initialize
+		@build << BuildDefault.new "autotools" do |recipe|
+			Dir.cd recipe.dirname
+
+			unless File.exists? "configure"
+				next Instructions::Status::Pass
+			end
+
+			child = Process.run("./configure",  ["--prefix=/package"], output: Process::Redirect::Inherit, error: Process::Redirect::Inherit)
+
+			if child.exit_status == 0
+				Instructions::Status::Success
+			else
+				Instructions::Status::Failed
+			end
+		end
+
+		@build << BuildDefault.new "make" do |recipe|
+			Dir.cd recipe.dirname
+
+			unless File.exists? "Makefile"
+				next Instructions::Status::Pass
+			end
+
+			child = Process.run("make", output: Process::Redirect::Inherit, error: Process::Redirect::Inherit)
+
+			if child.exit_status == 0
+				Instructions::Status::Success
+			else
+				Instructions::Status::Failed
+			end
+		end
 	end
 
-	def map(&block : Proc(String, Nil))
-		(configure + build + install).map &block
+	def to_a
+		[configure, build, install]
 	end
 end
 
diff --git a/src/main.cr b/src/main.cr
index c0e7e27..2fc8b25 100644
--- a/src/main.cr
+++ b/src/main.cr
@@ -13,11 +13,11 @@ Context.new().tap do |context|
 		recipe.download
 		recipe.extract
 
-		recipe.instructions.configure << "cd hello-#{recipe.version} && ./configure"
-		recipe.instructions.build << "cd hello-#{recipe.version} && make"
+		#recipe.instructions.configure << "cd hello-#{recipe.version} && ./configure"
+		#recipe.instructions.build << "cd hello-#{recipe.version} && make"
 		recipe.instructions.install << "cd hello-#{recipe.version} && make DESTDIR='${PKG}' install"
 
-		recipe.build
+		raise "oh no, build failed" unless recipe.build
 		recipe.package
 
 		recipe.clean
diff --git a/src/recipe.cr b/src/recipe.cr
index 40575b5..8ccf71c 100644
--- a/src/recipe.cr
+++ b/src/recipe.cr
@@ -20,6 +20,7 @@ class Package::Recipe
 
 	getter name : String
 	getter version : String
+	getter dirname : String?
 
 	getter sources : Sources
 	getter packages : Array(Package)
@@ -47,6 +48,10 @@ class Package::Recipe
 		"#{working_directory}/root"
 	end
 
+	def dirname
+		@dirname || "#{name}-#{version}"
+	end
+
 	def download
 		sources.map do |url|
 			unless File.exists? url.basename
@@ -73,15 +78,26 @@ class Package::Recipe
 	#     goes somehow wrong.
 	#   - Make things thread-safe. (those ENV[]= calls are definitely not)
 	def build
+		success = true
+
 		Dir.mkdir_p fake_root_directory
 
 		ENV["PKG"] = fake_root_directory
 
-		instructions.map do |script|
-			pp! Process.run "sh", ["-c", script], output: Process::Redirect::Inherit, error: Process::Redirect::Inherit, chdir: building_directory
+		old_dir = Dir.current
+
+		instructions.to_a.each do |instruction|
+			Dir.cd building_directory
+			if instruction.run(self).failed?
+				break Instructions::Status::Failed
+			end
 		end
 
+		Dir.cd old_dir
+
 		ENV["PKG"] = nil
+
+		success
 	end
 
 	def package