Resolve compact IRI conflict (var vs const)

Author: fogfish

doc/syntax.md

@@ -206,28 +206,17 @@ Goal defines a first rule.
 
 ## Semantic Web compatibility
 
-Semantic Web uses heavily IRIs as concept identifiers. This library implements datalog syntax enhancement  that support absolute and compact IRIs within the query. An absolute IRI is only used as literals but compact IRIs can be used as variables and literals simultaneously.
+Semantic Web heavily uses IRIs as identifiers. IRIs defines subjects, predicates and sometimes objects. This library implements datalog syntax enhancement that supports absolute and compact IRIs inside queries either as constants or variables.
 
-The following example shows usage of absolute IRI. You can use them as in-line literals within any predicates.
+IRIs as constants uses traditional syntax `<absolute IRI>` or `prefix:suffix`
 
 ```
-p(x, <http://example.com/1>).
-
 h(x) :- p(x, <http://example.com/1>).
+h(x) :- p(x, foaf:name).
 ```
 
-The following example shows usage of compact IRI, they are only allowed at ground truth or infix predicates.
-
-```
-p(x, foaf:name).
-
-h(x) :- p(x, y), y = foaf:name.
-```
-
-Any compact IRI within predicate is used as variable 
+Only compact IRIs are allowed as variable, they have to be prefixed by `'` character
 
 ```
-h(rdf:id, foaf:name) :- p(rdf:id, foaf:name).
+h('rdf:id, 'foaf:name) :- p('rdf:id, 'foaf:name).
 ```
-
-

src/datalog_leex.xrl

@@ -31,6 +31,9 @@ Rules.
 {CHAR}+  :
    {token, {symbol, TokenLine, TokenChars}}.
 
+'[a-zA-Z_:]* :
+   {token, {symbol, TokenLine, lists:sublist(TokenChars, 2, TokenLen - 1)}}.
+
 %%
 %% xsd:anyURI
 %%   <http://a/b> - absolute IRI

src/datalog_vm.erl

@@ -144,11 +144,6 @@ term(T, Predicate)
       #{T := Value} -> Value;
       _             -> '_'
    end;
-term({iri, _, _} = T, Predicate) ->
-   case Predicate of
-      #{T := Value} -> Value;
-      _             -> '_'
-   end;
 term(T, _) ->
    T.
 

test/datalog_SUITE.erl

@@ -206,7 +206,7 @@ recursion_3(_) ->
 %%
 source_semantic_web(_) ->
    datalog(
-      "?- schema:person(_, _). foaf:person(rdf:id, foaf:name). schema:person(rdf:id, foaf:name) :- foaf:person(rdf:id, foaf:name).",
+      "?- schema:person(_, _). foaf:person('rdf:id, 'foaf:name). schema:person('rdf:id, 'foaf:name) :- foaf:person('rdf:id, 'foaf:name).",
       [{1,2}, {2,3}, {3,4}],
       [{1,2}, {2,3}, {3,4}]
    ).