Re: [rules-dev] exploring functional programming

We are thinking of moving "accumulate" to a simple "for" keyword. We might allow 'in' and 'from' to be used interchangably and allow ';' semi colons to separate the sections. I'm also wondering ho we could allow function pipelines for the function part of the element. We also need type inference and "default" return values. So here are some code snippets to show what I'm thinking, as improvements over what we do with accumulate now. // Simple 'or' very simlar to accumulate before. ; for section

separating. With a new boolean section at the end to decide whether to propagate or not. Will probably use '=' for function assignments. $c : Customer() for( $bi : BasketItem( customer == $c ); $s = sum( $bi.price); $s> 100 ) // Multiple functions are ofcourse allowed $c : Customer() for( $bi : BasketItem( customer == $c ); $mn =min( $bi.price), $mx = max( $bi.price); ) // As are multiple patterns, and as before patterns can come 'from' an expression and with type inference we can get some nice compact text: for ( x in [0..4] y in [0..4] $c : Cell( row == y, col == x ); $avg = avg( $cell.value ); $avg> 100 ) The above is possible now with the following: Integer( this> 100) from accumulate( x : Integer() from [0, 1, 2, 3, 4] y : Integer() from [0, 1, 2, 3, 4], $c : Cell( row == y, col == x ), avg( $c.value) ) I think the proposed additions reall help with declarative readability. The normal chaining of elements is supported: $c : Customer() for( $b1 : BasketItem() in for( $b2 : BasketItem( customer == $c ); filter( $b2, $b2.price> 100); ); $a = avg( $b1.price ); ) 'for' will have a default return type for each bound function. In this case it returns a single value $a, if there are multiple bound results an array/map must be used for access. I also think we should allow pipelineing of functions, much as you would do in a normal functional programming, possibly using haskell like "stream fusion" capable functions. // '$' refers to the magic contents of the function which is "piped" in. So $bi is piped to map, $ refers to each value evaluated in the function, with type inference. 'map' results are piped to 'filter'. The final results are assigned to $r. $c : Customer() for( $bi : BasketItem( customer == $c ); $r = $bi | map( $, $.price * 2) | filter( $, $.price< 100); $r.size> 100 ) More ideas welcome :) But I think this opens up some very interesting areas for DRL, with something that will hopefully feel more natural for developers. Mark _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev