🤷 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/syntax/location.rs

@@ -0,0 +1,56 @@
+use codespan_reporting::diagnostic::{Diagnostic, Label};
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Location {
+    file_idx: usize,
+    offset: usize,
+}
+
+impl Location {
+    pub fn new(file_idx: usize, offset: usize) -> Self {
+        Location { file_idx, offset }
+    }
+
+    pub fn manufactured() -> Self {
+        Location {
+            file_idx: 0,
+            offset: 0,
+        }
+    }
+
+    pub fn primary_label(&self) -> Label<usize> {
+        Label::primary(self.file_idx, self.offset..self.offset)
+    }
+
+    pub fn secondary_label(&self) -> Label<usize> {
+        Label::secondary(self.file_idx, self.offset..self.offset)
+    }
+
+    pub fn range_label(&self, end: &Location) -> Vec<Label<usize>> {
+        if self.file_idx == end.file_idx {
+            vec![Label::primary(self.file_idx, self.offset..end.offset)]
+        } else if self.file_idx == 0 {
+            // if this is a manufactured item, then ... just try the other one
+            vec![Label::primary(end.file_idx, end.offset..end.offset)]
+        } else {
+            // we'll just pick the first location if this is in two different
+            // files
+            vec![Label::primary(self.file_idx, self.offset..self.offset)]
+        }
+    }
+
+    pub fn error(&self) -> Diagnostic<usize> {
+        Diagnostic::error().with_labels(vec![Label::primary(
+            self.file_idx,
+            self.offset..self.offset,
+        )])
+    }
+
+    pub fn labelled_error(&self, msg: &str) -> Diagnostic<usize> {
+        Diagnostic::error().with_labels(vec![Label::primary(
+            self.file_idx,
+            self.offset..self.offset,
+        )
+        .with_message(msg)])
+    }
+}