Function inside generic function doesn't work

[itryapitsin2]

This is a:

• Bug Report
• Feature Request
• Question
• Other

Which concerns:

• flow-runtime
• babel-plugin-flow-runtime
• flow-runtime-validators
• flow-runtime-mobx
• flow-config-parser
• The documentation website

---

What is the current behaviour?

type ActionTypes = { ... };
type THandlers<TState, TAction: ActionTypes> = {
    [key: string]: (state: TState, action: TAction) => TState
};

type TReducer<TState, TAction: ActionTypes> = (state: TState, action: TAction) => TState;

export default function createReducer<TState, TAction: ActionTypes>(
    initialState: TState,
    handlers: THandlers<TState, TAction>,
): TReducer<TState, TAction> {
    return function reducer(state: TState = initialState, action: TAction): TState {
        if (handlers[action.type]) {
            return handlers[action.type](state, action);
        }
        return state;
    };
}

This code throws exception that TAction and TState is not defined in line

return function reducer(state: TState = initialState, action: TAction): TState {

If change this codeline to

return function reducer(state: * = initialState, action: *): * {

then exception is missing and code works.

---

What is the expected behaviour?

Should work correctly.
Works fine without flow-runtime.

---

Which package versions are you using?

flow-runtime version: 0.17.0
babel-plugin-flow-runtime version: 0.18.0