Letrec. index in stdlib. fixing NaNs when measuring things without gaps, w or h. more window management stuff in OS

src/compiler.ts

@@ -71,8 +71,8 @@ export function compile(ast: AST, useStore = true, bound = new Set<string>(), to
 
         case 'let':
             const newBound = new Set([...bound, ast.name]);
-            return `((${sanitizeName(ast.name)}) =>
-                     ${compile(ast.body, useStore, newBound, topLevel)})(${compile(ast.value, useStore, bound, topLevel)})`;
+            return `(() => { let ${sanitizeName(ast.name)} = ${compile(ast.value, useStore, newBound, topLevel)};
+                return ${compile(ast.body, useStore, newBound, topLevel)}; })()`;
 
         case 'match':
             return compileMatch(ast, useStore, bound, topLevel);