🤷 The initial version of the compiler, both static and JIT.

This implements a full compiler, with both static compilation and JIT
support, for the world's simplest and silliest programming language. You
can do math, and print variables. That's it. On the bright side, it
implements every part of the compiler, from the lexer and parser;
through analysis and simplification; and into a reasonable code
generator. This should be a good jumping off point for adding more
advanced features.

Tests, including proptests, are included to help avoid regressions.

src/backend/error.rs

@@ -0,0 +1,46 @@
+use crate::backend::runtime::RuntimeFunctionError;
+use codespan_reporting::diagnostic::Diagnostic;
+use cranelift_codegen::{isa::LookupError, settings::SetError, CodegenError};
+use cranelift_module::ModuleError;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum BackendError {
+    #[error("Cranelift module error: {0}")]
+    Cranelift(#[from] ModuleError),
+    #[error("Builtin function error: {0}")]
+    BuiltinError(#[from] RuntimeFunctionError),
+    #[error("Internal variable lookup error")]
+    VariableLookupFailure,
+    #[error(transparent)]
+    CodegenError(#[from] CodegenError),
+    #[error(transparent)]
+    SetError(#[from] SetError),
+    #[error(transparent)]
+    LookupError(#[from] LookupError),
+}
+
+impl From<BackendError> for Diagnostic<usize> {
+    fn from(value: BackendError) -> Self {
+        match value {
+            BackendError::Cranelift(me) => {
+                Diagnostic::error().with_message(format!("Internal cranelift error: {}", me))
+            }
+            BackendError::BuiltinError(me) => {
+                Diagnostic::error().with_message(format!("Internal runtime function error: {}", me))
+            }
+            BackendError::VariableLookupFailure => {
+                Diagnostic::error().with_message("Internal variable lookup error!")
+            }
+            BackendError::CodegenError(me) => {
+                Diagnostic::error().with_message(format!("Internal codegen error: {}", me))
+            }
+            BackendError::SetError(me) => {
+                Diagnostic::error().with_message(format!("Internal backend setup error: {}", me))
+            }
+            BackendError::LookupError(me) => {
+                Diagnostic::error().with_message(format!("Internal error: {}", me))
+            }
+        }
+    }
+}