diff --git a/nac3core/src/lib.rs b/nac3core/src/lib.rs
index bff6b5c..f31dd35 100644
--- a/nac3core/src/lib.rs
+++ b/nac3core/src/lib.rs
@@ -1,7 +1,258 @@
 #![warn(clippy::all)]
 #![allow(dead_code)]
 
+use std::cmp::Ordering;
+use std::collections::hash_set::{IntoIter, Iter};
+use std::collections::HashSet;
+use self::Diagnostic::*;
+
+use std::fmt;
+use std::hash::{Hash, Hasher};
+use nac3parser::ast::Location;
+
 pub mod codegen;
 pub mod symbol_resolver;
 pub mod toplevel;
 pub mod typecheck;
+
+#[derive(Clone, Eq)]
+pub enum Diagnostic {
+    /// A diagnostic warning.
+    DiagWarn(String, Location),
+
+    /// A diagnostic error.
+    DiagErr(String, Location),
+}
+
+impl Diagnostic {
+
+    pub fn to_string(&self) -> String {
+
+        let diag_type = match self {
+            DiagErr(_, _) => "error",
+            DiagWarn(_, _) => "warning",
+        };
+        let msg = self.message();
+        let loc = self.location();
+
+        format!("{loc}: {diag_type}: {msg}")
+    }
+
+    /// Returns the message of this [Diagnostic].
+    fn message(&self) -> &str {
+        match self {
+            DiagErr(msg, _) => msg,
+            DiagWarn(msg, _) => msg,
+        }.as_str()
+    }
+
+    /// Returns the location of where this [Diagnostic] is created from.
+    fn location(&self) -> &Location {
+        match self {
+            DiagErr(_, loc) => loc,
+            DiagWarn(_, loc) => loc,
+        }
+    }
+}
+
+impl Ord for Diagnostic {
+    fn cmp(&self, other: &Self) -> Ordering {
+        let loc_cmp = self.location().cmp(other.location());
+        if loc_cmp != Ordering::Equal {
+            return loc_cmp
+        }
+
+        let diag_type_cmp = match self {
+            DiagWarn(_, _) => match other {
+                DiagWarn(_, _) => Ordering::Equal,
+                DiagErr(_, _) => Ordering::Less,
+            }
+
+            DiagErr(_, _) => match other {
+                DiagWarn(_, _) => Ordering::Greater,
+                DiagErr(_, _) => Ordering::Equal,
+            }
+        };
+        if diag_type_cmp != Ordering::Equal {
+            return diag_type_cmp
+        }
+
+        self.message().cmp(other.message())
+    }
+}
+
+impl PartialOrd for Diagnostic {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl PartialEq for Diagnostic {
+    fn eq(&self, other: &Self) -> bool {
+        match self {
+            DiagErr(msg, loc) => {
+                if let DiagErr(other_msg, other_loc) = other {
+                    msg == other_msg && loc == other_loc
+                } else {
+                    false
+                }
+            }
+
+            DiagWarn(msg, loc) => {
+                if let DiagWarn(other_msg, other_loc) = other {
+                    msg == other_msg && loc == other_loc
+                } else {
+                    false
+                }
+            }
+        }
+    }
+}
+
+impl fmt::Display for Diagnostic {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.to_string())
+    }
+}
+
+impl Hash for Diagnostic {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.to_string().hash(state)
+    }
+}
+
+#[deprecated]
+pub fn contains_errors(diagnostics: &HashSet<Diagnostic>) -> bool {
+    diagnostics.iter().any(|d| match d {
+        DiagErr(_, _) => true,
+        _ => false,
+    })
+}
+
+/// Type alias for [Result] encapsulating a success value of type [T], and any diagnostics emitted
+/// during the generation of the result.
+///
+/// This type should be used where a result cannot be meaningfully generated when a subset of the
+/// possible diagnostics is emitted.
+pub type DiagnosticsResult<T> = Result<(T, DiagnosticEngine), DiagnosticEngine>;
+
+/// Type representing a result of type `T` with any diagnostics emitted during the generation of the
+/// result.
+///
+/// This type should be used where, even when diagnostics are generated, a meaningful result can
+/// still be generated.
+pub struct DiagnosticsPartialResult<T> {
+    value: T,
+    engine: DiagnosticEngine,
+}
+
+impl <T> Into<DiagnosticsResult<T>> for DiagnosticsPartialResult<T> {
+    fn into(self) -> DiagnosticsResult<T> {
+        if self.engine.has_errors() {
+            Err(self.engine)
+        } else {
+            Ok((self.value, self.engine))
+        }
+    }
+}
+
+/// A simple abstraction over a set of collected diagnostics.
+#[derive(Clone, Default)]
+pub struct DiagnosticEngine {
+    diagnostics: HashSet<Diagnostic>,
+}
+
+impl DiagnosticEngine {
+    pub fn new() -> DiagnosticEngine {
+        Self::default()
+    }
+
+    pub fn from(s: HashSet<Diagnostic>) -> DiagnosticEngine {
+        DiagnosticEngine {
+            diagnostics: s
+        }
+    }
+    
+    pub fn single(diag: Diagnostic) -> DiagnosticEngine {
+        Self::from(HashSet::from([diag]))
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.diagnostics.is_empty()
+    }
+
+    pub fn has_errors(&self) -> bool {
+        self.diagnostics.iter().any(|d| match d {
+            DiagErr(_, _) => true,
+            _ => false,
+        })
+    }
+
+    pub fn insert(&mut self, diag: Diagnostic) {
+        self.diagnostics.insert(diag);
+    }
+    
+    pub fn extend<I: IntoIterator<Item = Diagnostic>>(&mut self, diags: I) {
+        self.diagnostics.extend(diags);
+    }
+
+    pub fn merge_with(&mut self, other: DiagnosticEngine) {
+        self.extend(other.diagnostics)
+    }
+
+    pub fn consume_partial_result<T>(&mut self, result: DiagnosticsPartialResult<T>) -> T {
+        self.merge_with(result.engine);
+        result.value
+    }
+
+    pub fn consume_result<T>(&mut self, result: DiagnosticsResult<T>) -> Result<T, Self> {
+        match result {
+            Ok((v, diags)) => {
+                self.merge_with(diags);
+                Ok(v)
+            }
+
+            Err(diags) => {
+                self.merge_with(diags);
+                Err(self.clone())
+            }
+        }
+    }
+
+    pub fn consume_result_to_option<T>(&mut self, result: DiagnosticsResult<T>) -> Option<T> {
+        match result {
+            Ok((v, diags)) => {
+                self.merge_with(diags);
+                Some(v)
+            }
+
+            Err(diags) => {
+                self.merge_with(diags);
+                None
+            }
+        }
+    }
+
+    pub fn iter(&self) -> Iter<'_, Diagnostic> {
+        self.diagnostics.iter()
+    }
+
+    pub fn into_iter(self) -> IntoIter<Diagnostic> {
+        self.diagnostics.into_iter()
+    }
+
+    pub fn into_partial_result<T>(self, value: T) -> DiagnosticsPartialResult<T> {
+        DiagnosticsPartialResult {
+            value,
+            engine: self
+        }
+    }
+
+    pub fn into_result<T>(self, value: T) -> DiagnosticsResult<T> {
+        if self.has_errors() {
+            Err(self)
+        } else {
+            Ok((value, self))
+        }
+    }
+}