Extract variable management, move into `state` package

1 files changed, 48 insertions, 0 deletions

diff --git a/source/state/stack.d b/source/state/stack.d
new file mode 100644
index 0000000..3c6230f
--- /dev/null
+++ b/source/state/stack.d
@@ -0,0 +1,48 @@
+module state.stack;
+
+import std.conv;
+import std.string;
+import std.variant;
+import std.container : SList;
+
+alias Token = Algebraic!(int, bool, string);
+alias Stack = SList;
+
+Stack!Token stack;
+
+Token toToken(string value) {
+	if ( value.isNumeric ) {
+		return Token(parse!int(value));
+	} else {
+		return Token(value);
+	}
+}
+
+Token top(ref Stack!Token stack) {
+	if ( stack.empty ) {
+		throw new Exception("stack is empty");
+	} else {
+		return stack.front;
+	}
+}
+
+Token pop(ref Stack!Token stack) {
+	Token token = stack.top;
+	stack.removeFront;
+	return token;
+}
+
+template push(T)
+if ( is(T == int) || is(T == bool) || is (T == string) ) {
+	void push(ref Stack!Token stack, T value) {
+		stack.push(Token(value));
+	}
+}
+
+void push(ref Stack!Token stack, Token token) {
+	stack.insertFront(token);
+}
+
+void push(ref Stack!Token stack, Stack!Token prefix) {
+	stack.insertFront(prefix[]);
+}