From d45207342cff211679a8194f0aa6f7edaf0e7216 Mon Sep 17 00:00:00 2001
From: Yura Dupyn <2153100+omedusyo@users.noreply.github.com>
Date: Sat, 7 Feb 2026 14:57:01 +0100
Subject: [PATCH] strict ts + fixes

---
 src/lang/debug/expr_show.ts    |  1 +
 src/lang/debug/repl.ts         |  2 +-
 src/lang/debug/value_show.ts   |  3 +--
 src/lang/parser/cursor.test.ts |  1 +
 src/lang/parser/cursor.ts      | 11 +++++------
 src/lang/parser/scanner.ts     |  2 +-
 src/lang/parser/source_text.ts |  2 +-
 src/lang/value.ts              |  2 +-
 tsconfig.json                  |  3 +++
 9 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/lang/debug/expr_show.ts b/src/lang/debug/expr_show.ts
index db78fe5..08acf9f 100644
--- a/src/lang/debug/expr_show.ts
+++ b/src/lang/debug/expr_show.ts
@@ -1,3 +1,4 @@
+// AI GENERATED
 import { Expr, Pattern, ProductPattern, Literal, FieldAssignment, FieldPattern } from '../value';
 
 export function exprToString(expr: Expr): string {
diff --git a/src/lang/debug/repl.ts b/src/lang/debug/repl.ts
index 3980e10..efd8f6b 100644
--- a/src/lang/debug/repl.ts
+++ b/src/lang/debug/repl.ts
@@ -1,3 +1,4 @@
+// AI GENERATED
 import * as readline from 'readline';
 import * as fs from 'fs';
 import { parse, ParseError } from '../parser/parser';
@@ -155,7 +156,6 @@ function getErrorMessage(err: ParseError): string {
         case "UnicodeUnclosed": return "Unicode escape missing closing brace '}'.";
         case "UnicodeOverflow": return `Unicode code point ${err.reason.value.toString(16)} is out of bounds.`;
       }
-      return "Invalid escape sequence.";
 
     // Context specific errors
     case "ExpectedExpression": return "Expected an expression here.";
diff --git a/src/lang/debug/value_show.ts b/src/lang/debug/value_show.ts
index 7c13080..a59b859 100644
--- a/src/lang/debug/value_show.ts
+++ b/src/lang/debug/value_show.ts
@@ -1,5 +1,4 @@
-// src/debug/value_string.ts
-
+// AI GENERATED
 import { Value, Env, Closure, EnvFrame } from '../value';
 import { exprToString, productPatternToString } from './expr_show';
 
diff --git a/src/lang/parser/cursor.test.ts b/src/lang/parser/cursor.test.ts
index 2a3b09e..ae32bf8 100644
--- a/src/lang/parser/cursor.test.ts
+++ b/src/lang/parser/cursor.test.ts
@@ -1,3 +1,4 @@
+// AI GENERATED
 import { SourceText } from "./source_text";
 import { Cursor, scanString, scanNumber } from "./cursor";
 import { Result } from "../result";
diff --git a/src/lang/parser/cursor.ts b/src/lang/parser/cursor.ts
index a5a5e5f..f89242c 100644
--- a/src/lang/parser/cursor.ts
+++ b/src/lang/parser/cursor.ts
@@ -147,16 +147,12 @@ export function scanNumber(cursor: Cursor): Result<{ value: number, span: Span }
 
   const startNumberLocation = cursor.currentLocation();
 
-  let c: CodePoint;
-
   // 1. Optional Sign
-  c = cursor.peek();
-  if (c === char("-")) {
+  if (cursor.peek() === char("-")) {
     cursor.next();
   }
 
   // 2. Integer Part
-  c = cursor.peek();
   const integerPartDigitCount = cursor.consumeWhile(isDigit);
   if (integerPartDigitCount === 0) {
     return Result.error({
@@ -238,7 +234,10 @@ export function scanString(cursor: Cursor): Result<{ value: string, span: Span }
       // 2. Escape Sequences
       const escapeStart = cursor.currentLocation();
       cursor.next(); // consume backslash
-      const escaped = cursor.peek();
+      if (cursor.eof()) {
+        return Result.error({ tag: "UnexpectedEOF", span: cursor.makeSpan(start) });
+      }
+      const escaped = cursor.peek() as CodePoint; // it can't be `undefined`
       
       switch (escaped) {
         case char('n'): value += '\n'; cursor.next(); break;
diff --git a/src/lang/parser/scanner.ts b/src/lang/parser/scanner.ts
index c1bd3c8..757397f 100644
--- a/src/lang/parser/scanner.ts
+++ b/src/lang/parser/scanner.ts
@@ -97,7 +97,7 @@ export type PatternStartToken =
 function rawIdentifier(cursor: Cursor): string {
   const start = cursor.currentIndex;
   while (!cursor.eof()) {
-    const c = cursor.peek();
+    const c = cursor.peek() as CodePoint;
 
     if (DELIMITER_SET.has(c) || isWhitespace(c)) {
       break;
diff --git a/src/lang/parser/source_text.ts b/src/lang/parser/source_text.ts
index bea2545..6a32584 100644
--- a/src/lang/parser/source_text.ts
+++ b/src/lang/parser/source_text.ts
@@ -5,7 +5,7 @@ export type CodePointIndex = number; // index into array of code-points
 export type CodePoint = number; // could also name it `UnicodeCodePoint`. Basically for `s: string` we have `s.codePointAt(i: index): char`.
 
 export function char(c: string): CodePoint {
-  return c.codePointAt(0)
+  return c.codePointAt(0) as CodePoint;
 }
 
 export type CodePointRef = {
diff --git a/src/lang/value.ts b/src/lang/value.ts
index ae5bd56..e1a3e2a 100644
--- a/src/lang/value.ts
+++ b/src/lang/value.ts
@@ -333,7 +333,7 @@ export function eval_start(program: Program, e: Expr): Result<Value> {
     return Result.ok(eval_expr(program, Env.nil(), e));
   } catch (err) {
     if (typeof err === "object" && (err as any).kind === "RuntimeError") {
-      return Result.error(err.error as RuntimeError);
+      return Result.error((err as ThrownRuntimeError).error);
     } else {
       throw err;
     }
diff --git a/tsconfig.json b/tsconfig.json
index 74434b2..2ad79ef 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -9,6 +9,9 @@
     "sourceMap": true,
     "baseUrl": ".",
     "outDir": "dist",
+    "strict": true,
+    "noFallthroughCasesInSwitch": true,
+    "noImplicitReturns": true,
     "moduleResolution": "node",
     "resolveJsonModule": true
   }