2 files changed, 31 insertions, 19 deletions
diff --git a/src/lib/core/common.ts b/src/lib/core/common.ts
index b5f494e..8cff899 100644
--- a/src/lib/core/common.ts
+++ b/src/lib/core/common.ts
@@ -38,7 +38,12 @@ export type ASTNode<
   Type extends NodeType = NodeType,
   Name extends string = string,
   Value extends any = any,
-  Children extends ASTNode[] = ASTNode<NodeType, string, any, any>[]
+  Children extends readonly ASTNode[] = readonly ASTNode<
+    NodeType,
+    string,
+    any,
+    any
+  >[]
 > = {
   type: Type;
   name: Name;
diff --git a/src/lib/core/eval.ts b/src/lib/core/eval.ts
index 7c2c91b..10cc23c 100644
--- a/src/lib/core/eval.ts
+++ b/src/lib/core/eval.ts
@@ -9,7 +9,7 @@ export type ToStringInner<T, Carry extends string = ""> = T extends
   | number
   ? `${T}`
   : T extends readonly any[]
-  ? T extends [infer Head, ...infer Tail]
+  ? T extends readonly [infer Head, ...infer Tail]
     ? `${ToStringInner<
         Tail,
         `${Carry extends "" ? "" : `${Carry}, `}${ToStringInner<Head>}`
@@ -17,11 +17,22 @@ export type ToStringInner<T, Carry extends string = ""> = T extends
     : `[${Carry}]`
   : FnError<`Can't stringify`>;
 
-export type BUILTIN_ToString<Args extends readonly ASTNode[]> = {
-  [Idx in Exclude<keyof Args, keyof any[]>]: Args[Idx] extends ASTNode
-    ? ToStringInner<Evaluate<Args[Idx]>>
-    : never;
-};
+export type UnarrayIfOnlyHead<T extends readonly any[]> = T extends [
+  infer Head,
+  infer Next
+]
+  ? T
+  : T extends [infer Head]
+  ? Head
+  : T;
+
+export type BUILTIN_ToString<Args extends readonly ASTNode[]> = ToStringInner<
+  UnarrayIfOnlyHead<{
+    [Idx in keyof Args]: Args[Idx] extends ASTNode
+      ? ToStringInner<Evaluate<Args[Idx]>>
+      : never;
+  }>
+>;
 // export type BUILTIN_Print<Args extends readonly ASTNode[]>
 
 export type SENTINEL_NO_BUILTIN = "__NO_BUILTIN__";
@@ -34,22 +45,18 @@ export type EvalError<T extends string> = `Eval error: ${T}`;
 export type Evaluate<Node extends ASTNode> = Node["type"] extends NodeType.INT
   ? Node["value"]
   : Node["type"] extends NodeType.ROOT
-  ? {
-      // FIXME render as array??
-      [Idx in Exclude<
-        keyof Node["children"],
-        keyof any[]
-      >]: Node["children"][Idx] extends ASTNode
-        ? Evaluate<Node["children"][Idx]>
-        : never;
-      // indexing for now to remove object syntax
-      // pls fix
-    }[Exclude<keyof Node["children"], keyof any[]>]
+  ? Node["children"] extends infer Children extends readonly ASTNode[]
+    ? UnarrayIfOnlyHead<{
+        [Idx in keyof Children]: Children[Idx] extends ASTNode
+          ? Evaluate<Children[Idx]>
+          : never;
+      }>
+    : EvalError<`Unexpected error parsing children of ${Node["type"]}`>
   : Node["type"] extends NodeType.EXT
   ? MapBuiltins<Node>
   : EvalError<`Unhandled node type ${Node["type"]}`>;
 
-const input = `tostring(5, 3)` as const;
+const input = `tostring(5, 2)` as const;
 const lex_result = null as unknown as Lex<typeof input>;
 const parse_result = null as unknown as Parse<typeof lex_result>;
 const eval_result = null as unknown as Evaluate<typeof parse_result>;