Macro lambda 

macro_rules! lambda {
    {let $n:ident = |$($an:ident $(: $at:path)*),+| -> $o:ty { $($s:stmt);* }} => { ... };
    {let $n:ident$(<$($p:ident $(: $pb:path)*),+>)*($($c:ident: $ct:ty)+) = |$($an:ident $(: $at:path)*),+| -> $o:ty { $($s:stmt);* }} => { ... };
}

This macro can be used to define lambdas with syntax similar to rust’s lambdas Arguments are bounded by traits Mainly to use with Functor and Foldable