Add support for evaluation context

For now it acts as just the value mode that can be enabled anywhere
variable expansion is supported, for example:

(foo=bar):

And the primary use currently is to enable/test quoted and indirect
variable expansion:

"foo bar" = FOO BAR
print $"foo bar"    # Invalid.
print $("foo bar")  # Yeah, baby.

foo = FOO
FOO = foo
print $($foo)

Not that you should do something like this...

9 files changed, 72 insertions, 1 deletions

diff --git a/tests/eval/buildfile b/tests/eval/buildfile
new file mode 100644
index 0000000..c658d3b
--- /dev/null
+++ b/tests/eval/buildfile
@@ -0,0 +1,13 @@
+(./):
+
+# Invalid.
+#
+#(foo
+#(foo #comment
+
+print ()
+print ((foo)(bar))
+print ((foo)   (bar))
+
+print (foo\
+bar)
diff --git a/tests/eval/test.out b/tests/eval/test.out
new file mode 100644
index 0000000..5885c7d
--- /dev/null
+++ b/tests/eval/test.out
@@ -0,0 +1,4 @@
+
+foobar
+foo bar
+foobar
diff --git a/tests/eval/test.sh b/tests/eval/test.sh
new file mode 100755
index 0000000..b898b3c
--- /dev/null
+++ b/tests/eval/test.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+valgrind -q b -q | diff -u test.out -
diff --git a/tests/lexer/driver.cxx b/tests/lexer/driver.cxx
index a3819f5..ca27d39 100644
--- a/tests/lexer/driver.cxx
+++ b/tests/lexer/driver.cxx
@@ -89,7 +89,7 @@ main ()
   assert (lex ("\"foo \"\"bar\"") == tokens ({"foo bar", ""}));
   assert (lex ("foo\" \"bar") == tokens ({"foo bar", ""}));
   assert (lex ("\"foo\nbar\"") == tokens ({"foo\nbar", ""}));
-  assert (lex ("\"#:{}()=+\n\"") == tokens ({"#:{}()=+\n", ""}));
+  assert (lex ("\"#:{})=+\n\"") == tokens ({"#:{})=+\n", ""}));
   assert (lex ("\"'\"") == tokens ({"'", ""}));
   assert (lex ("\"\\\"") == tokens ({"\\", ""}));
 
diff --git a/tests/quote/buildfile b/tests/quote/buildfile
index 6dd22b4..19c2bfc 100644
--- a/tests/quote/buildfile
+++ b/tests/quote/buildfile
@@ -19,4 +19,14 @@ print $foo'bar'
 print $foo"$bar"
 print "$foo"bar
 
+# Quoting and evaluation context.
+#
+print ("x{foo bar}")
+#print "(x{foo bar})" # multiple values in concatenating context expansion
+print "({foo})"
+print "('foo bar')"
+print "("foo bar")"
+print "("$foo bar")"
+print "("$foo ($bar)")"
+
 ./:
diff --git a/tests/quote/test.out b/tests/quote/test.out
index 216b1c8..f5d7a71 100644
--- a/tests/quote/test.out
+++ b/tests/quote/test.out
@@ -12,3 +12,9 @@ fo o bar
 fo obar
 fo o bar 
 fo obar
+x{foo bar}
+foo
+foo bar
+foo bar
+fo o bar
+fo o  bar 
diff --git a/tests/variable/expansion/buildfile b/tests/variable/expansion/buildfile
new file mode 100644
index 0000000..3f28372
--- /dev/null
+++ b/tests/variable/expansion/buildfile
@@ -0,0 +1,26 @@
+foo = FOO
+
+print $foo
+print $(foo)
+
+# Invalid.
+#
+#print $
+#print $()
+#print $(foo bar)
+#print $(foo{bar})
+
+# Indirect.
+#
+FOO = foo
+print $($FOO)
+print $($(FOO))
+print $($($FOO))
+
+# Quoted name.
+#
+"b a r" = BAR
+print $("b a r")
+#print $"b a r"
+
+./:
diff --git a/tests/variable/expansion/test.out b/tests/variable/expansion/test.out
new file mode 100644
index 0000000..5056f04
--- /dev/null
+++ b/tests/variable/expansion/test.out
@@ -0,0 +1,6 @@
+FOO
+FOO
+FOO
+FOO
+foo
+BAR
diff --git a/tests/variable/expansion/test.sh b/tests/variable/expansion/test.sh
new file mode 100755
index 0000000..b898b3c
--- /dev/null
+++ b/tests/variable/expansion/test.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+valgrind -q b -q | diff -u test.out -