add two more tutorials

tutorial/01_constraints.py

@@ -0,0 +1,92 @@
+# We now make our meta-model more interesting by adding a 'price' attribute to B, and constraints to it.
+
+mm_cs = """
+    # class named 'A':
+    A:Class
+
+    # class named 'B':
+    B:Class {
+        constraint = ```
+            # Price must be less than 100
+            get_value(get_slot(this, "price")) < 100 
+        ```;
+    }
+
+    # 'B' has an attribute 'price':
+    B_price:AttributeLink (B -> Integer) {
+        name = "price";
+        optional = False;
+    }
+
+    # An association from 'A' to 'B':
+    a2b:Association (A -> B) {
+        # Every 'A' must be associated with at least one 'B'
+        target_lower_cardinality = 1;
+    }
+
+    totalPriceLessThan500:GlobalConstraint {
+        constraint = ```
+            total_price = 0;
+            for b_name, b_id in get_all_instances("B"):
+                total_price += get_value(get_slot(b_id, "price"))
+            total_price < 500
+        ```;
+    }
+"""
+
+####
+# Note: The name 'B_price' follows a fixed format: <class_name>_<attribute_name>.
+#  This format must be followed!
+####
+
+# We update our model to include a price:
+
+m_cs = """
+    myA:A
+
+    myB:B {
+        price = 1000;
+    }
+
+    myLnk:a2b (myA -> myB)
+"""
+
+
+# And do a conformance check:
+
+from state.devstate import DevState
+from bootstrap.scd import bootstrap_scd
+from concrete_syntax.textual_od import parser
+from framework.conformance import Conformance, render_conformance_check_result
+
+state = DevState()
+print("Loading meta-meta-model...")
+mmm = bootstrap_scd(state)
+print("OK")
+
+print()
+print("Parsing meta-model...")
+mm = parser.parse_od(
+    state,
+    m_text=mm_cs, # the string of text to parse
+    mm=mmm, # the meta-model of class diagrams (= our meta-meta-model)
+)
+print("OK")
+
+print()
+print("Parsing model...")
+m = parser.parse_od(
+    state,
+    m_text=m_cs,
+    mm=mm, # this time, the meta-model is the previous model we parsed
+)
+print("OK")
+
+print()
+print("Is our model a valid instance of our meta model?")
+conf = Conformance(state, m, mm)
+print(render_conformance_check_result(conf.check_nominal()))
+
+# Can you fix the constraint violation?
+
+