FCM

App.re

<TextField
  icon=(module IconOk)
  value
  onChange=change
/>

Icon.re

module type Component = {
  [@react.component]
  let make: (~color: Color.t, ~className: string=?) => React.element;
};

[@react.component]
let make = (~className="", ~children) => {
  <Svg className={...}>
    children
  </Svg>
};

IconOk.re

[@react.component]
let make = (~color, ~className=?) => {
  <Icon size ?className>
    <path fill={color->Icon.Color.toString} />
  </Icon>
};

TextField.re

[@react.component]
let make =
    (
      ~value: string,
      ~icon: option(module Icon.Component)=?,
      ~onChange: option(ReactEvent.Form.t => unit)=?,
    ) =>
  <>
    <input value ?onChange />
    {
      switch (icon) {
      | Some(icon) =>
        let (module Icon) = icon;
        <Icon color={...} />;
      | None => React.null
      }
    }
  </>;