Error Messaging Redesign

This commit contains the following:

* New data types to support full tracebacks
* New traceback data type used across stl and ast
* Updates to tests
* fixes for error messaging in sym and some stl functions

src/error.rs

@@ -0,0 +1,99 @@
+/* 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::fmt;
+
+#[derive(Debug, Clone)]
+pub struct TraceItem {
+    pub caller:  String,
+    pub message: String,
+}
+
+#[derive(Debug, Clone)]
+pub struct Traceback(pub Vec<TraceItem>);
+
+pub fn start_trace(item: TraceItem) -> Traceback {
+    Traceback::new().with_trace(item)
+}
+
+impl Traceback {
+    pub fn new() -> Traceback {
+        Traceback(vec![])
+    }
+
+    pub fn with_trace(&self, item: TraceItem) -> Traceback {
+        let mut next = Traceback(self.0.clone());
+        next.0.push(item);
+        next
+    }
+
+    pub fn depth(&self) -> usize {
+        self.0.len()
+    }
+}
+
+impl fmt::Display for Traceback {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        _ = writeln!(f, "** ERROR TRACEBACK");
+        for trace in self.0.iter().rev() {
+            _ = writeln!(f, " > {}: {}", trace.caller, trace.message);
+        }
+        writeln!(f, "Please refactor forms and try again...")
+    }
+}
+
+impl std::convert::Into<String> for Traceback {
+    fn into(self) -> String {
+        format!("{}", self)
+    }
+}
+
+impl std::convert::From<(&String, &str)> for TraceItem {
+    fn from(value: (&String, &str)) -> Self {
+        TraceItem {
+            caller:  value.0.clone(),
+            message: String::from(value.1),
+        }
+    }
+}
+
+impl std::convert::From<(&String, String)> for TraceItem {
+    fn from(value: (&String, String)) -> Self {
+        TraceItem {
+            caller: value.0.clone(),
+            message: value.1,
+        }
+    }
+}
+
+impl std::convert::From<(&str, String)> for TraceItem {
+    fn from(value: (&str, String)) -> Self {
+        TraceItem {
+            caller: String::from(value.0),
+            message: value.1,
+        }
+    }
+}
+
+impl std::convert::From<(&str, &str)> for TraceItem {
+    fn from(value: (&str, &str)) -> Self {
+        TraceItem {
+            caller: String::from(value.0),
+            message: String::from(value.1),
+        }
+    }
+}