Supporting empty programs in datalog languages, fixes pr11140

collects/datalog/parse.rkt

@@ -31,7 +31,7 @@
                            (datum->syntax #f tok-value (make-srcloc start-pos end-pos)))))
     (grammar
      (program [(statements) $1])
-     (statements [(statement) (list $1)]
+     (statements [() empty]
                  [(statement statements) (list* $1 $2)])
      (statement [(assertion) $1]
                 [(query) $1]

collects/datalog/stx.rkt

@@ -38,6 +38,7 @@
     [(_ thy-expr stmt ...)
      (syntax/loc stx
        (parameterize ([current-theory thy-expr])
+         (void)
          (->substitutions
           (datalog-stmt-var-selector stmt)
           (eval-statement (datalog-stmt stmt)))
@@ -48,6 +49,7 @@
     [(_ thy-expr stmt ...)
      (syntax/loc stx
        (parameterize ([current-theory thy-expr])
+         (void)
          (eval-top-level-statement (datalog-stmt stmt))
          ...))]))
 

collects/tests/datalog/examples/empty.rkt

@@ -0,0 +1 @@
+#lang datalog

collects/tests/datalog/paren-examples/empty.rkt

@@ -0,0 +1 @@
+#lang datalog/sexp