some stuff

src/error.ts

@@ -0,0 +1,74 @@
+export type Span = {
+  start: number;
+  end: number;
+};
+
+export class CompilerError extends Error {
+  msg: string;
+  span: Span;
+
+  constructor(msg: string, span: Span) {
+    super(msg);
+    this.msg = msg;
+    this.span = span;
+  }
+}
+
+export function withErrorHandler(input: string, f: () => void) {
+  try {
+    f();
+  } catch (e) {
+    if (e instanceof CompilerError) {
+      renderError(input, e);
+    } else {
+      throw e;
+    }
+  }
+}
+
+function renderError(input: string, e: CompilerError) {
+  const lineSpans = lines(input);
+  const line =
+    e.span.start === Number.MAX_SAFE_INTEGER
+      ? lineSpans[lineSpans.length - 1]
+      : lineSpans.find(
+          (line) => line.start <= e.span.start && line.end >= e.span.start
+        );
+  if (!line) {
+    throw Error(`Span out of bounds: ${e.span.start}..${e.span.end}`);
+  }
+  const lineIdx = lineSpans.indexOf(line);
+  console.error(`error: ${e.message}`);
+
+  console.error(`${lineIdx} | ${spanToSnippet(input, line)}`);
+  const startRelLine =
+    e.span.start === Number.MAX_SAFE_INTEGER ? 0 : e.span.start - line.start;
+  console.error(
+    `${" ".repeat(String(lineIdx).length)}   ${" ".repeat(startRelLine)}^`
+  );
+}
+
+function spanToSnippet(input: string, span: Span): string {
+  if (span.start === Number.MAX_SAFE_INTEGER) {
+    return "";
+  }
+  return input.slice(span.start, span.end);
+}
+
+export function lines(input: string): Span[] {
+  const lines: Span[] = [{ start: 0, end: 0 }];
+
+  for (let i = 0; i < input.length; i++) {
+    if (input[i] === "\n") {
+      lines.push({ start: i + 1, end: i + 1 });
+    } else {
+      lines[lines.length - 1].end++;
+    }
+  }
+
+  return lines;
+}
+
+export function todo(msg: string, span: Span): never {
+  throw new CompilerError(`TODO: ${msg}`, span);
+}