Improve astToString, add tests for astToString

dev/test/astUtils.test.ts

@@ -0,0 +1,18 @@
+import { describe, it} from "mocha";
+import type { astToString } from "../../src/parse/ast/utils.js";
+import { attest } from "../attest/main.js";
+
+describe('astToString', () => {
+    it('no parentheses if nested ast is an array', () => {
+        const t = {} as unknown as astToString<[["number", "[]"], "|", "number"]>
+        attest(t).typed as "'number[]|number'"
+    });
+    it('parentheses if nested ast is an infix expression', () => {
+        const t = {} as unknown as astToString<[["0", "|", "1"], "|", "string"]>
+        attest(t).typed as "'(0|1)|string'"
+    });
+    it('defaults to "..." if input is bad', () => {
+        const t = {} as unknown as astToString<["0", "///", "1"]>
+        attest(t).typed as "'...'"
+    });
+});

src/parse/ast/utils.ts

@@ -1,12 +1,25 @@
-import type { Literalable } from "../../utils/generics.js"
+import type { List, Literalable } from "../../utils/generics.js"
+import type { Scanner } from "../string/shift/scanner.js"
+import type { InfixExpression, PostfixExpression } from "./ast.js"
 
-export type astToString<ast> = `'${astToStringRecurse<ast, "">}'`
-
-type astToStringRecurse<ast, result extends string> = ast extends [
-    infer head,
-    ...infer tail
-]
-    ? astToStringRecurse<tail, `${result}${astToStringRecurse<head, "">}`>
+export type astToString<ast> = `'${astToStringRecurse<ast>}'`;
+
+type astToStringRecurse<ast> = 
+    ast extends PostfixExpression<infer operator, infer operand>
+        ? operator extends "[]"
+            ? `${groupAst<operand>}[]`
+            : never
+    : ast extends InfixExpression<infer operator, infer l, infer r>
+        ? operator extends "&" | "|" | "%" | Scanner.Comparator
+            ? `${groupAst<l>}${operator}${groupAst<r>}`
+            : never
     : ast extends Literalable
-    ? `${result}${ast extends bigint ? `${ast}n` : ast}`
-    : "..."
+        ? `${ast extends bigint ? `${ast}n` : ast}`
+        : "..."
+
+
+type groupAst<ast> = ast extends List 
+    ? ast[1] extends "[]" 
+        ? astToStringRecurse<ast> 
+        : `(${astToStringRecurse<ast>})` 
+    : astToStringRecurse<ast>