Macro gtmpl::gtmpl_fn

macro_rules! gtmpl_fn {
    (
        $(#[$outer:meta])*
        fn $name:ident() -> Result<$otyp:ty, String>
        { $($body:tt)* }
    ) => { ... };
    (
        $(#[$outer:meta])*
        fn $name:ident($arg0:ident : $typ0:ty) -> Result<$otyp:ty, String>
        { $($body:tt)* }
    ) => { ... };
    (
        $(#[$outer:meta])*
        fn $name:ident($arg0:ident : $typ0:ty$(, $arg:ident : $typ:ty)*) -> Result<$otyp:ty, String>
        { $($body:tt)* }
    ) => { ... };
}

Help to write new functions for gtmpl.