Implement few builtin functions that can operate on any value

type()
null()
empty ()
identity()

9 files changed, 117 insertions, 5 deletions

diff --git a/build2/buildfile b/build2/buildfile
index fa6faef..98494d8 100644
--- a/build2/buildfile
+++ b/build2/buildfile
@@ -15,6 +15,7 @@ exe{b}:                                                 \
             {hxx ixx     cxx}{ file                   } \
             {hxx     txx cxx}{ filesystem             } \
             {hxx         cxx}{ function               } \
+            {            cxx}{ functions-builtin      } \
             {            cxx}{ functions-path         } \
 	    {            cxx}{ functions-process-path } \
             {hxx         cxx}{ lexer                  } \
diff --git a/build2/function b/build2/function
index 68edcde..192c4a3 100644
--- a/build2/function
+++ b/build2/function
@@ -37,7 +37,8 @@ namespace build2
   // T           - statically-typed (value_traits<T> must be defined)
   // names       - untyped
   // value       - any type
-  // T*          - NULL-able argument (here T can be names, value).
+  // T*          - NULL-able argument (here T can be names)
+  // value*      - NULL-able any type (never NULL itself, use value::null)
   // optional<T> - optional argument (here T can be T*, names, value)
   //
   // Optional arguments must be last. In case of a failure the function is
@@ -281,6 +282,15 @@ namespace build2
     }
   };
 
+  template <>
+  struct function_arg<value*>: function_arg<value>
+  {
+    static const bool null = true;
+
+    static value*
+    cast (value* v) {return v;} // NULL indicator in value::null.
+  };
+
   template <typename T>
   struct function_arg<optional<T>>: function_arg<T>
   {
diff --git a/build2/function.cxx b/build2/function.cxx
index 46dc403..e76f0c2 100644
--- a/build2/function.cxx
+++ b/build2/function.cxx
@@ -295,6 +295,7 @@ namespace build2
   //
   function_map functions;
 
+  void builtin_functions ();       // functions-builtin.cxx
   void path_functions ();          // functions-path.cxx
   void process_path_functions ();  // functions-process-path.cxx
 
@@ -302,6 +303,7 @@ namespace build2
   {
     functions_init ()
     {
+      builtin_functions ();
       path_functions ();
       process_path_functions ();
     }
diff --git a/build2/functions-builtin.cxx b/build2/functions-builtin.cxx
new file mode 100644
index 0000000..448bb53
--- /dev/null
+++ b/build2/functions-builtin.cxx
@@ -0,0 +1,24 @@
+// file      : build2/functions-builtin.cxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <build2/function>
+#include <build2/variable>
+
+using namespace std;
+
+namespace build2
+{
+  void
+  builtin_functions ()
+  {
+    function_family f ("builtin");
+
+    f["type"] = [](value* v) {return v->type != nullptr ? v->type->name : "";};
+
+    f["null"]  = [](value* v) {return v->null;};
+    f["empty"] = [](value v)  {return v.empty ();};
+
+    f["identity"] = [](value* v) {return move (*v);};
+  }
+}
diff --git a/tests/function/buildfile b/tests/function/buildfile
index 52288ca..6c26737 100644
--- a/tests/function/buildfile
+++ b/tests/function/buildfile
@@ -2,6 +2,6 @@
 # copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
 # license   : MIT; see accompanying LICENSE file
 
-d = path/
+d = builtin/ path/
 ./: $d
 include $d
diff --git a/tests/function/builtin/buildfile b/tests/function/builtin/buildfile
new file mode 100644
index 0000000..5a49ad0
--- /dev/null
+++ b/tests/function/builtin/buildfile
@@ -0,0 +1,7 @@
+# file      : tests/function/builtin/buildfile
+# copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+# license   : MIT; see accompanying LICENSE file
+
+./: test{testscript}
+
+test{*}: test = $effect($build.path)
diff --git a/tests/function/builtin/testscript b/tests/function/builtin/testscript
new file mode 100644
index 0000000..1a4c5d1
--- /dev/null
+++ b/tests/function/builtin/testscript
@@ -0,0 +1,68 @@
+# file      : tests/function/path/testscript
+# copyright : Copyright (c) 2014-2016 Code Synthesis Ltd
+# license   : MIT; see accompanying LICENSE file
+
++mkdir build
++cat <<EOI >>>build/bootstrap.build
+project = test
+amalgamation =
+EOI
+
+test.options += -q --buildfile - noop
+
+: type
+:
+{
+  $* <'print $type([string])'      >'string'  : empty-typed
+  $* <'print $type("")'            >''        : empty-untyped
+
+  $* <'print $type([string null])' >'string'  : null-typed
+  $* <'print $type([null])'        >''        : null-untyped
+
+  $* <'print $type([string] abc)'  >'string'  : value-typed
+  $* <'print $type(abc)'           >''        : value-untyped
+}
+
+: null
+:
+{
+  $* <'print $null("")'     >'false'       : empty
+  $* <'print $null(abc)'    >'false'       : value
+  $* <'print $null([null])' >'true'        : null
+}
+
+: empty
+:
+{
+  $* <<EOI     >'true'                       : empty-untyped
+  x =
+  print \$empty\(\$x)
+  EOI
+
+  $* <'print $empty([string])'     >'true'   : empty-typed
+  $* <'print $empty(abc)'          >'false'  : name
+  $* <'print $empty(abc cxx{foo})' >'false'  : names
+  $* <'print $empty([bool] false)' >'false'  : bool
+}
+
+: identity
+:
+{
+  $* <'print       $identity([string])'        >'';
+  $* <'print $type($identity([string]))'       >'string'   : empty-typed
+
+  $* <'print       $identity("")'              >'{}';
+  $* <'print $type($identity(""))'             >''         : empty-untyped
+
+  $* <'print       $identity([string null])'   >'[null]';
+  $* <'print $type($identity([string null]))'  >'string'   : null-typed
+
+  $* <'print       $identity([null])'          >'[null]';
+  $* <'print $type($identity([null]))'         >''         : null-untyped
+
+  $* <'print       $identity([string] abc)'    >'abc';
+  $* <'print $type($identity([string] abc))'   >'string'   : null-typed
+
+  $* <'print       $identity(abc)'             >'abc';
+  $* <'print $type($identity(abc))'            >''         : null-untyped
+}
diff --git a/unit-tests/function/buildfile b/unit-tests/function/buildfile
index 1efc7e1..756fbcd 100644
--- a/unit-tests/function/buildfile
+++ b/unit-tests/function/buildfile
@@ -7,8 +7,8 @@
 import libs = libbutl%lib{butl}
 src = token lexer diagnostics utility variable name b-options types-parsers \
 context scope parser target operation rule prerequisite file module function \
-functions-path functions-process-path algorithm search dump filesystem \
-config/{utility init operation}
+functions-builtin functions-path functions-process-path algorithm search dump \
+filesystem config/{utility init operation}
 
 exe{driver}: cxx{driver} ../../build2/cxx{$src} $libs test{call syntax}
 
diff --git a/unit-tests/test/script/parser/buildfile b/unit-tests/test/script/parser/buildfile
index 5025e60..6cc319a 100644
--- a/unit-tests/test/script/parser/buildfile
+++ b/unit-tests/test/script/parser/buildfile
@@ -7,7 +7,7 @@
 import libs = libbutl%lib{butl}
 src = token lexer parser diagnostics utility variable name context target \
 scope prerequisite file module operation rule b-options algorithm search \
-filesystem function functions-path functions-process-path \
+filesystem function functions-builtin functions-path functions-process-path \
 config/{utility init operation} dump types-parsers test/{target \
 script/{token lexer parser script}}