tried some modifier tricks, this is good enough as is

src/contracts/modifiers/apply.ts

@@ -0,0 +1,48 @@
+import type {ContractInputGeneric, ContractState} from '../types';
+
+/**
+ * Apply allows one to execute modifiers which are functions that are run
+ * before the function body is executed, similar to [Solidity modifiers](https://docs.soliditylang.org/en/latest/contracts.html#function-modifiers).
+ *
+ * The first three arguments are mandatory, and the remaining arguments are expected to be modifier functions. These modifiers
+ * will run in the order they appear, and if all pass, a result with the same type of the input is returned.
+ *
+ * For example, consider a function call with the following type:
+ *
+ * ```ts
+ * {
+ *    function: "divide",
+ *    value: {
+ *      a: number,
+ *      b: number,
+ *    }
+ * }
+ * ```
+ *
+ * We take two numbers and return `a/b`. We can write a modifier to ensure `b` is non-zero.
+ *
+ * ```ts
+ * const {a, b} = await apply(caller, input.value, state,
+ *   (caller, input, state) => {
+ *     if (input.b === 0) {
+ *       throw new Error("denominator cant be zero");
+ *     }
+ *     return input;
+ *   }
+ * );
+ * ```
+ *
+ * Due to the generic template parameters, when `apply` is used within the switch-case of the `handle` function, it gets type-safety
+ * based on which function is being handled!
+ */
+export async function apply<I extends ContractInputGeneric['value'], S extends ContractState>(
+  caller: string,
+  input: I,
+  state: S,
+  ...modifiers: ((caller: string, input: I, state: S) => I | Promise<I>)[]
+): Promise<typeof input> {
+  for (const modifier of modifiers) {
+    input = await modifier(caller, input, state);
+  }
+  return input;
+}

src/contracts/modifiers/index.ts

@@ -1,3 +1,5 @@
+export {apply} from './apply';
+
 import {ExpectedProofError, InvalidProofError, NotOwnerError, NotWhitelistedError, NullValueError} from '../errors';
 import {verifyProof} from '../utils';
 import {ContractState} from '../types';
@@ -77,50 +79,3 @@ export const onlyProofVerified = <I extends {key: string; value?: unknown; proof
     return input;
   };
 };
-
-/**
- * Apply allows one to execute modifiers which are functions that are run
- * before the function body is executed, similar to [Solidity modifiers](https://docs.soliditylang.org/en/latest/contracts.html#function-modifiers).
- *
- * The first three arguments are mandatory, and the remaining arguments are expected to be modifier functions. These modifiers
- * will run in the order they appear, and if all pass, a result with the same type of the input is returned.
- *
- * For example, consider a function call with the following type:
- *
- * ```ts
- * {
- *    function: "divide",
- *    value: {
- *      a: number,
- *      b: number,
- *    }
- * }
- * ```
- *
- * We take two numbers and return `a/b`. We can write a modifier to ensure `b` is non-zero.
- *
- * ```ts
- * const {a, b} = await apply(caller, input.value, state,
- *   (caller, input, state) => {
- *     if (input.b === 0) {
- *       throw new Error("denominator cant be zero");
- *     }
- *     return input;
- *   }
- * );
- * ```
- *
- * Due to the generic template parameters, when `apply` is used within the switch-case of the `handle` function, it gets type-safety
- * based on which function is being handled!
- */
-export async function apply<I, S extends ContractState>(
-  caller: string,
-  input: I,
-  state: S,
-  ...modifiers: ((caller: string, input: I, state: S) => I | Promise<I>)[]
-): Promise<typeof input> {
-  for (const modifier of modifiers) {
-    input = await modifier(caller, input, state);
-  }
-  return input;
-}