Implement value typing, null support via value attributes

For example:

v = [null]
v = [string] abc
v += ABC # abcABC

2 files changed, 72 insertions, 4 deletions

diff --git a/tests/variable/type/buildfile b/tests/variable/type/buildfile
index 372b0ad..85c18e1 100644
--- a/tests/variable/type/buildfile
+++ b/tests/variable/type/buildfile
@@ -1,5 +1,13 @@
 # Variable typing.
 #
+
+#[string] str3 = foo
+#[bool] str3 = false       # error: changing str3 type from string to bool
+
+#[bool string] str3 = foo  # error: multiple variable types: bool, string
+
+#[junk] jnk = foo          # error: unknown variable attribute junk
+
 [string] str1 = bar
 str1 =+ foo
 str1 += baz
@@ -10,12 +18,63 @@ str2 = bar
 str2 += baz
 print $str2
 
-#[string] str3 = foo
-#[bool] str3 = false       # error: changing str3 type from string to bool
+# Value typing.
+#
 
-#[bool string] str3 = foo  # error: multiple variable types: bool, string
+#v = [bool string] true # error: multiple value types: string, bool
+#v = [string=junk] true # error: unexpected value for attribute string: junk
 
-#[junk] jnk = foo          # error: unknown variable attribute junk
+#[string] var =
+#var = [bool] true # error: confliction variable var type string and value type bool
+
+#var = [string] false
+#var += [bool] true # error: confliction original value type string and append/prepend value type bool
+
+v1a = [uint64] 00
+v1b += [uint64] 00
+v1c =+ [uint64] 00
+print $v1a $v1b $v1c # 0 0 0
+
+v2 = [uint64] 00
+v2 = [string] 00
+print $v2 # 00
+
+#v3a = [uint64] 00
+#v3a += [string] 00 # error: confliction original value type uint64 and append/prepend value type string
+
+#v3b = [uint64] 00
+#v3b =+ [string] 00 # error: confliction original value type uint64 and append/prepend value type string
+
+v4a = 01
+v4a += [uint64] 01
+print $v4a # 2
+
+v4b = 01
+v4b =+ [uint64] 01
+print $v4b # 2
+
+v5a = 01
+sub/:
+{
+  v5a += [uint64] 01
+  print $v5a # 2
+}
+
+v5b = 01
+sub/:
+{
+  v5b =+ [uint64] 01
+  print $v5b # 2
+}
+
+v6 = [uint64 null]
+v6 += 00
+print $v6 # 0
+
+v7 = [string null]
+v7 += [uint64] 00
+print $v7 # 0
 
+print [uint64] 00 # 0
 
 ./:
diff --git a/tests/variable/type/test.out b/tests/variable/type/test.out
index f5dfb84..4aea91f 100644
--- a/tests/variable/type/test.out
+++ b/tests/variable/type/test.out
@@ -1,2 +1,11 @@
 foobarbaz
 foobarbaz
+0 0 0
+00
+2
+2
+2
+2
+0
+0
+0