Draft: Resolve "Short circuiting and lazy evaluation"

Closes #49

src/virtmat/language/constraints/chem.py

@@ -2,8 +2,7 @@
 from textx import get_children_of_type, textx_isinstance
 from virtmat.language.utilities.textx import get_reference
 from virtmat.language.utilities.errors import StaticValueError, raise_exception
-from virtmat.language.utilities.errors import issue_warning
-from virtmat.language.utilities.warnings import TextSUserWarning
+from virtmat.language.utilities.warnings import warnings, TextSUserWarning
 from virtmat.language.utilities.chemistry import is_equation_balanced
 
 
@@ -25,7 +24,7 @@ def check_chem_reaction_balance(react, metamodel):
     if len(lcomps+rcomps) != len(react.educts+react.products):
         msg = ('reaction balance check skipped due to missing '
                'composition in some terms')
-        issue_warning(react, TextSUserWarning, msg)
+        warnings.warn(TextSUserWarning(msg, obj=react))
         return
     if not is_equation_balanced(lcomps, lcoeff, rcomps, rcoeff):
         msg = ('Reaction equation is not balanced. Check '