Add string_set buildfile value type

This exposes the std::set<std::string> type to buildfiles.

New functions:

  $size(<string-set>)

Subscript returns true if the value is present and false otherwise (so
it is mapped to std::set::contains()). For example:

set = [string_set] a b c

if ($set[b])
  ...

Note that append (+=) and prepend (=+) have the same semantics
(std::set::insert()). For example:

set = [string_set] a b
set += c b              # a b c
set =+ d b              # a b c d

Example of iteration:

set = [string_set] a b c
for k: $set
  ...

2 files changed, 56 insertions, 0 deletions

diff --git a/tests/type/set/buildfile b/tests/type/set/buildfile
new file mode 100644
index 0000000..55b37bb
--- /dev/null
+++ b/tests/type/set/buildfile
@@ -0,0 +1,4 @@
+# file      : tests/type/set/buildfile
+# license   : MIT; see accompanying LICENSE file
+
+./: testscript $b
diff --git a/tests/type/set/testscript b/tests/type/set/testscript
new file mode 100644
index 0000000..3897220
--- /dev/null
+++ b/tests/type/set/testscript
@@ -0,0 +1,52 @@
+# file      : tests/type/set/testscript
+# license   : MIT; see accompanying LICENSE file
+
+# See also tests in function/*/ (size()).
+
+.include ../../common.testscript
+
+: basics
+:
+$* <<EOI >>EOO
+s = [string_set] a b a
+print $s
+s += c b
+print $s
+s =+ d b
+print $s
+EOI
+a b
+a b c
+a b c d
+EOO
+
+: type
+:
+$* <<EOI >>EOO
+s = [string_set]
+print $type($s)
+EOI
+string_set
+EOO
+
+: subscript
+:
+$* <<EOI >>EOO
+s = [string_set] a b c
+print ($s[b])
+print ($s[z])
+EOI
+true
+false
+EOO
+
+: iteration
+:
+$* <<EOI >>EOO
+for s: [string_set] a b c
+  print $s
+EOI
+a
+b
+c
+EOO