Add vars table

- added vars table
- refactored function and func table to use impl
- added add and delete methods for func table

src/vars.rs

@@ -0,0 +1,47 @@
+/* relish: versatile lisp shell
+ * Copyright (C) 2021 Aidan Hahn
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+use std::boxed::Box;
+use std::collections::HashMap;
+use crate::cell::{Ctr, Cell};
+
+/* Mapping between a string token and a tree of Cells
+ * The string token can be found in any Ctr::Symbol value
+ *
+ * Considerations: should I use a structure of cells for this?
+ * Current thoughts: if this was a language without proper data types, yes.
+ */
+pub type VTable = HashMap<String, Cell>;
+
+impl VTable {
+    pub fn define(
+        &mut self,
+        identifier: String,
+        var_tree: Box<Cell>
+    ) {
+        if let Some(boxed_cell) = self.insert(identifier, var_tree) {
+            drop(boxed_cell);
+        }
+    }
+
+    pub fn get(
+        &self,
+        identifier: String
+    ) -> Option<Box<Cell>> {
+        self.get(identifier)
+    }
+}