Question

Here is some gramma wich represents tree

<tree> -> *
<tree> -> (<tree><tree>)

where * means leaf and couple of trees in parentheses describes root that sons are trees in parentheses.
i Have to rewrite that gramma to dcg and add semantic actions which will create abstrac tree of that tree whith leaf/0 and node/2 example node(node(leaf,leaf),node(leaf,leaf))
for any idea or source i will be gratefull.

Answer 1

This works in my SWI-Prolog:

leaf_rule(leaf) --> "*".
tree_rule(X) --> leaf_rule(X), !.
tree_rule(node(X,Y)) --> "(", tree_rule(X), tree_rule(Y), ")".

In order to parse a string you need to call phrase predicate, for example:

phrase(tree_rule(X), "((**)*)", Rest).

Prolog will unify X with abstract representation of tree from string.