Math helper nearly done, test almost passes.

src/renderer/parameters_context.rs

@@ -68,6 +68,16 @@ impl<'a> ParametersContext<'a> {
         }
     }
 
+    pub fn from_values(
+        parent: Option<&'a ParametersContext<'a>>,
+        params: HashMap<&'a str, Option<BreadcrumbTreeElement<'a>>>,
+    ) -> Self {
+        ParametersContext {
+            parent: parent,
+            params: params,
+        }
+    }
+
     pub fn contains_key(&self, segment: &str) -> bool {
         self.params.contains_key(segment)
             || self

src/renderer/renderer.rs

@@ -665,15 +665,54 @@ impl<'a> DustRenderer<'a> {
                             })
                             .unwrap_or(Ok("".to_owned()));
                     }
-                    Some(_) => {
-                        // TODO: math with body, calculate the value and use it like a select block
+                    Some(body) => {
                         // Calculate the value
-                        let calculated_value = self.perform_math_operation(breadcrumbs, &param_map);
-                        // Generate a ParametersContext with the result of the math operation as key
+                        let calculated_value =
+                            match self.perform_math_operation(breadcrumbs, &param_map) {
+                                None => return Ok("".to_owned()),
+                                Some(val) => val,
+                            };
 
+                        // Generate a ParametersContext with the result of the math operation as key
+                        let converted_value: BreadcrumbTreeElement<'_> = calculated_value.into();
+                        let calculated_param_map: HashMap<&str, Option<BreadcrumbTreeElement<'_>>> =
+                            vec![("key", Some(converted_value))].into_iter().collect();
+                        let calculated_context =
+                            ParametersContext::from_values(None, calculated_param_map);
                         // calculate are_any_checks_true
+                        let are_any_checks_true = body
+                            .elements
+                            .iter()
+                            .filter_map(|te| match te {
+                                TemplateElement::TETag(dt) => match dt {
+                                    DustTag::DTHelperEquals(_)
+                                    | DustTag::DTHelperNotEquals(_)
+                                    | DustTag::DTHelperGreaterThan(_)
+                                    | DustTag::DTHelperLessThan(_)
+                                    | DustTag::DTHelperGreaterThanOrEquals(_)
+                                    | DustTag::DTHelperLessThanOrEquals(_) => Some(dt),
+                                    _ => None,
+                                },
+                                _ => None,
+                            })
+                            .map(|dt| {
+                                self.perform_comparison_check(
+                                    dt,
+                                    new_breadcrumbs_ref,
+                                    Some(&calculated_context),
+                                )
+                            })
+                            .any(|check_result| check_result.unwrap_or(false));
                         // Generate a SelectContext
+                        let select_context =
+                            SelectContext::new(&calculated_context, are_any_checks_true);
                         // render_maybe_body
+                        return self.render_maybe_body(
+                            &parameterized_block.contents,
+                            new_breadcrumbs_ref,
+                            blocks,
+                            &mut Some(select_context),
+                        );
                     }
                 }
             }