Added basic implentation for where

tests/non_reg/test_sheerka_non_reg.py

@@ -273,8 +273,9 @@ as:
 
         saved_definitions = sheerka.sdp.get_safe(sheerka.CONCEPTS_DEFINITIONS_ENTRY)
         expected_bnf = Sequence(
-            a, Optional(Sequence(StrMatch("plus"), ConceptExpression("plus", rule_name="plus"))))
-        assert saved_definitions[saved_concept] == expected_bnf
+            ConceptExpression(a, rule_name="a"),
+            Optional(Sequence(StrMatch("plus"), ConceptExpression(saved_concept, rule_name="plus"))))
+        assert saved_definitions["c:plus|1001:"] == "(c:a:=a ('plus' c:plus|1001:=plus)?)"
 
         new_concept = res[0].value.body
         assert new_concept.metadata.name == "plus"
@@ -456,6 +457,26 @@ as:
         assert res[0].status
         assert res[0].body == 23
 
+    def test_i_can_mix_bnf_and_isa_when_concept_other_case(self):
+        sheerka = self.get_sheerka()
+
+        init = [
+            "def concept one as 1",
+            "def concept twenty as 20",
+            "def concept number",
+            "one isa number",
+            "twenty isa number",
+            "def concept twenties from bnf twenty number as twenty + number"
+        ]
+
+        for exp in init:
+            sheerka.evaluate_user_input(exp)
+
+        res = sheerka.evaluate_user_input("twenty one")
+        assert len(res) == 1
+        assert res[0].status
+        assert res[0].body == simplec("twenties", 21)
+
     def test_i_can_mix_concept_of_concept(self):
         sheerka = self.get_sheerka()
 
@@ -623,3 +644,30 @@ as:
         assert len(res) == 1
         assert res[0].status
         assert res[0].body == 21
+
+    def test_i_can_use_where_in_bnf(self):
+        sheerka = self.get_sheerka()
+
+        init = [
+            "def concept one as 1",
+            "def concept two as 2",
+            "def concept three as 3",
+            "def concept twenty as 20",
+            "def concept number",
+            "one isa number",
+            "two isa number",
+            "three isa number",
+            "def concept twenties from bnf twenty number where number <= 2 as twenty + number"
+        ]
+
+        for exp in init:
+            sheerka.evaluate_user_input(exp)
+
+        res = sheerka.evaluate_user_input("eval twenty one")
+        assert len(res) == 1 and res[0].status and res[0].body == 21
+
+        res = sheerka.evaluate_user_input("eval twenty two")
+        assert len(res) == 1 and res[0].status and res[0].body == 22
+
+        res = sheerka.evaluate_user_input("eval twenty three")
+        assert len(res) > 1