12 files changed, 138 insertions, 126 deletions
diff --git a/src/lang/builtin/index.ts b/src/lang/builtin/index.ts
new file mode 100644
index 0000000..373f54a
--- /dev/null
+++ b/src/lang/builtin/index.ts
@@ -0,0 +1,34 @@
+import {
+  AddNumbers,
+  AddStrings,
+  Multiply,
+  ToString,
+  UnarrayIfOnlyHead,
+} from "../util";
+
+export type FnError<T extends string> = `Function execution error: ${T}`;
+
+export type BUILTIN_Arr<Args extends readonly any[]> = Args;
+
+export type BUILTIN_ToString<Args extends readonly any[]> = ToString<
+  UnarrayIfOnlyHead<{
+    [Idx in keyof Args]: ToString<Args[Idx]>;
+  }>
+>;
+
+export type BUILTIN_Add<Args extends readonly any[]> =
+  Args extends readonly string[]
+    ? AddStrings<Args>
+    : Args extends readonly number[]
+    ? AddNumbers<Args>
+    : FnError<`Cannot add operands ${ToString<Args>}`>;
+
+export type BUILTIN_Mul<Args extends readonly any[]> = Args extends [
+  infer A,
+  infer B,
+  infer C
+]
+  ? FnError<`Can only multiply [number, number], but got ${ToString<Args>}`>
+  : Args extends [infer M extends number, infer N extends number]
+  ? Multiply<M, N>
+  : FnError<`Can only multiply [number, number], but got ${ToString<Args>}`>;
diff --git a/src/lib/core/common.ts b/src/lang/core/common.ts
index c1a1dc3..c1a1dc3 100644
--- a/src/lib/core/common.ts
+++ b/src/lang/core/common.ts
diff --git a/src/lang/core/eval.ts b/src/lang/core/eval.ts
new file mode 100644
index 0000000..6a25a6c
--- /dev/null
+++ b/src/lang/core/eval.ts
@@ -0,0 +1,42 @@
+import {
+  BUILTIN_Add,
+  BUILTIN_Arr,
+  BUILTIN_Mul,
+  BUILTIN_ToString,
+} from "../builtin";
+import { ASTNode, NodeType } from "./common";
+import { Lex } from "./lexer";
+import { Parse } from "./parser";
+
+export type SENTINEL_NO_BUILTIN = "__NO_BUILTIN__";
+export type MapBuiltins<Node extends ASTNode> =
+  Node["children"] extends infer Children extends readonly ASTNode[]
+    ? {
+        [Idx in keyof Children]: Children[Idx] extends ASTNode
+          ? Evaluate<Children[Idx]>
+          : never;
+      } extends infer Args extends readonly any[]
+      ? Node["name"] extends "tostring"
+        ? BUILTIN_ToString<Args>
+        : Node["name"] extends "arr"
+        ? BUILTIN_Arr<Args>
+        : Node["name"] extends "add"
+        ? BUILTIN_Add<Args>
+        : Node["name"] extends "mul"
+        ? BUILTIN_Mul<Args>
+        : SENTINEL_NO_BUILTIN
+      : never
+    : never;
+
+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.EXT
+  ? MapBuiltins<Node>
+  : EvalError<`Unhandled node type ${Node["type"]}`>;
+
+const input = `` 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>;
diff --git a/src/lib/core/index.ts b/src/lang/core/index.ts
index e69de29..e69de29 100644
--- a/src/lib/core/index.ts
+++ b/src/lang/core/index.ts
diff --git a/src/lib/core/lexer.ts b/src/lang/core/lexer.ts
index 33a408a..33a408a 100644
--- a/src/lib/core/lexer.ts
+++ b/src/lang/core/lexer.ts
diff --git a/src/lib/core/parser.ts b/src/lang/core/parser.ts
index 79218e9..79218e9 100644
--- a/src/lib/core/parser.ts
+++ b/src/lang/core/parser.ts
diff --git a/src/lib/index.ts b/src/lang/index.ts
index 8d119de..8d119de 100644
--- a/src/lib/index.ts
+++ b/src/lang/index.ts
diff --git a/src/lang/util/index.ts b/src/lang/util/index.ts
new file mode 100644
index 0000000..00a3e54
--- /dev/null
+++ b/src/lang/util/index.ts
@@ -0,0 +1,3 @@
+export * from "./number";
+export * from "./utils";
+export * from "./string";
diff --git a/src/lang/util/number.ts b/src/lang/util/number.ts
new file mode 100644
index 0000000..132994b
--- /dev/null
+++ b/src/lang/util/number.ts
@@ -0,0 +1,34 @@
+export type NumberToArray<
+  Number extends number,
+  Carry extends readonly any[] = []
+> = Number extends Carry["length"]
+  ? Carry
+  : NumberToArray<Number, [...Carry, any]>;
+
+export type NumbersToArray<
+  Numbers extends readonly number[],
+  Carry extends readonly any[] = []
+> = Numbers extends [
+  infer Head extends number,
+  ...infer Tail extends readonly number[]
+]
+  ? NumbersToArray<Tail, [...Carry, ...NumberToArray<Head>]>
+  : Carry;
+
+export type AddNumbers<Numbers extends readonly number[]> =
+  NumbersToArray<Numbers> extends infer T extends readonly any[]
+    ? T["length"]
+    : never;
+
+export type MultiplyInner<
+  N extends number,
+  MS extends readonly any[],
+  Carry extends number = 0
+> = MS extends [infer Head extends number, ...infer Tail extends readonly any[]]
+  ? MultiplyInner<N, Tail, AddNumbers<[Carry, N]>>
+  : Carry;
+
+export type Multiply<M extends number, N extends number> = MultiplyInner<
+  M,
+  NumberToArray<N>
+>;
diff --git a/src/lang/util/string.ts b/src/lang/util/string.ts
new file mode 100644
index 0000000..5772f40
--- /dev/null
+++ b/src/lang/util/string.ts
@@ -0,0 +1,17 @@
+export type AddStrings<
+  Strings extends readonly string[],
+  Carry extends string = ""
+> = Strings extends [infer Head extends string, ...infer Tail extends string[]]
+  ? AddStrings<Tail, `${Carry}${Head}`>
+  : Carry;
+
+export type ToString<T, Carry extends string = ""> = T extends string | number
+  ? `${T}`
+  : T extends readonly any[]
+  ? T extends readonly [infer Head, ...infer Tail]
+    ? `${ToString<
+        Tail,
+        `${Carry extends "" ? "" : `${Carry}, `}${ToString<Head>}`
+      >}`
+    : `[${Carry}]`
+  : never;
diff --git a/src/lang/util/utils.ts b/src/lang/util/utils.ts
new file mode 100644
index 0000000..ac36ca1
--- /dev/null
+++ b/src/lang/util/utils.ts
@@ -0,0 +1,8 @@
+export type UnarrayIfOnlyHead<T extends readonly any[]> = T extends [
+  infer Head,
+  infer Next
+]
+  ? T
+  : T extends [infer Head]
+  ? Head
+  : T;
diff --git a/src/lib/core/eval.ts b/src/lib/core/eval.ts
deleted file mode 100644
index 59cda1d..0000000
--- a/src/lib/core/eval.ts
+++ /dev/null
@@ -1,126 +0,0 @@
-import { ASTNode, NodeType } from "./common";
-import { Lex } from "./lexer";
-import { Parse } from "./parser";
-
-export type FnError<T extends string> = `Function execution error: ${T}`;
-
-export type ToStringInner<T, Carry extends string = ""> = T extends
-  | string
-  | number
-  ? `${T}`
-  : T extends readonly any[]
-  ? T extends readonly [infer Head, ...infer Tail]
-    ? `${ToStringInner<
-        Tail,
-        `${Carry extends "" ? "" : `${Carry}, `}${ToStringInner<Head>}`
-      >}`
-    : `[${Carry}]`
-  : FnError<`Can't stringify`>;
-
-export type UnarrayIfOnlyHead<T extends readonly any[]> = T extends [
-  infer Head,
-  infer Next
-]
-  ? T
-  : T extends [infer Head]
-  ? Head
-  : T;
-
-export type NumberToArray<
-  Number extends number,
-  Carry extends readonly any[] = []
-> = Number extends Carry["length"]
-  ? Carry
-  : NumberToArray<Number, [...Carry, any]>;
-
-export type NumbersToArray<
-  Numbers extends readonly number[],
-  Carry extends readonly any[] = []
-> = Numbers extends [
-  infer Head extends number,
-  ...infer Tail extends readonly number[]
-]
-  ? NumbersToArray<Tail, [...Carry, ...NumberToArray<Head>]>
-  : Carry;
-
-export type AddNumbers<Numbers extends readonly number[]> =
-  NumbersToArray<Numbers> extends infer T extends readonly any[]
-    ? T["length"]
-    : never;
-
-export type AddStrings<
-  Strings extends readonly string[],
-  Carry extends string = ""
-> = Strings extends [infer Head extends string, ...infer Tail extends string[]]
-  ? AddStrings<Tail, `${Carry}${Head}`>
-  : Carry;
-
-export type MultiplyInner<
-  N extends number,
-  MS extends readonly any[],
-  Carry extends number = 0
-> = MS extends [infer Head extends number, ...infer Tail extends readonly any[]]
-  ? MultiplyInner<N, Tail, AddNumbers<[Carry, N]>>
-  : Carry;
-export type Multiply<M extends number, N extends number> = MultiplyInner<
-  M,
-  NumberToArray<N>
->;
-
-export type BUILTIN_Arr<Args extends readonly any[]> = Args;
-
-export type BUILTIN_ToString<Args extends readonly any[]> = ToStringInner<
-  UnarrayIfOnlyHead<{
-    [Idx in keyof Args]: ToStringInner<Args[Idx]>;
-  }>
->;
-
-export type BUILTIN_Add<Args extends readonly any[]> =
-  Args extends readonly string[]
-    ? AddStrings<Args>
-    : Args extends readonly number[]
-    ? AddNumbers<Args>
-    : FnError<`Cannot add operands ${ToStringInner<Args>}`>;
-
-export type BUILTIN_Mul<Args extends readonly any[]> = Args extends [
-  infer A,
-  infer B,
-  infer C
-]
-  ? FnError<`Can only multiply [number, number], but got ${ToStringInner<Args>}`>
-  : Args extends [infer M extends number, infer N extends number]
-  ? Multiply<M, N>
-  : FnError<`Can only multiply [number, number], but got ${ToStringInner<Args>}`>;
-
-export type SENTINEL_NO_BUILTIN = "__NO_BUILTIN__";
-export type MapBuiltins<Node extends ASTNode> =
-  Node["children"] extends infer Children extends readonly ASTNode[]
-    ? {
-        [Idx in keyof Children]: Children[Idx] extends ASTNode
-          ? Evaluate<Children[Idx]>
-          : never;
-      } extends infer Args extends readonly any[]
-      ? Node["name"] extends "tostring"
-        ? BUILTIN_ToString<Args>
-        : Node["name"] extends "arr"
-        ? BUILTIN_Arr<Args>
-        : Node["name"] extends "add"
-        ? BUILTIN_Add<Args>
-        : Node["name"] extends "mul"
-        ? BUILTIN_Mul<Args>
-        : SENTINEL_NO_BUILTIN
-      : never
-    : never;
-
-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.EXT
-  ? MapBuiltins<Node>
-  : EvalError<`Unhandled node type ${Node["type"]}`>;
-
-const input = `` 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>;