Initial structure for the perform_math_operation function.

js/test_cases/helpers_math/README.md

@@ -2,3 +2,8 @@ Early termination
 -----------------
 
 If the math helper has a body then it stops rendering conditionals after the first conditional that returns true. Rendering an else block does not cause early termination, but else blocks are rendered.
+
+Non-number values
+-----------------
+
+If the math operation involves non-numbers, NaN is returned.

js/test_cases/helpers_math/input1.json

@@ -1,5 +1,7 @@
 {
   "number_7": 7,
   "string_7": "7",
-  "string_cat": "cat"
+  "string_cat": "cat",
+  "add_operation": "add",
+  "a_operation": "a"
 }

js/test_cases/helpers_math/main.dust

@@ -4,6 +4,7 @@ Bodiless math{~n}
 {@math key=number_7 method="add" operand="4" /}{~n}
 {@math key=string_7 method="add" operand="4" /}{~n}
 {@math key=string_cat method="add" operand="4" /}{~n}
+{@math key=string_cat method="add" operand="foo" /}{~n}
 
 Math with body: dot reference{~n}
 ============================={~n}
@@ -44,15 +45,67 @@ Math with body: standalone else block{~n}
 Math with body: early termination{~n}
 ============================={~n}
 {@math key="7" method="add" operand="4"}
-    {@eq value=11}math result is 11{:else}math result is not 11{/eq}{~n}
-    {@eq value=11}math result is 11{:else}math result is not 11{/eq}{~n}
+    {@eq value=11}math result is 11{~n}{:else}math result is not 11{~n}{/eq}
+    {@eq value=11}math result is 11{~n}{:else}math result is not 11{~n}{/eq}
 {/math}
 
 Math with body: early termination else block{~n}
 ============================================{~n}
 {@math key="7" method="add" operand="4"}
-    {@eq value=12}math result is 12{:else}math result is not 12{/eq}{~n}
-    {@eq value=11}math result is 11{:else}math result is not 11{/eq}{~n}
-    {@eq value=12}math result is 12{:else}math result is not 12{/eq}{~n}
+    {@eq value=12}math result is 12{~n}{:else}math result is not 12{~n}{/eq}
+    {@eq value=11}math result is 11{~n}{:else}math result is not 11{~n}{/eq}
+    {@eq value=12}math result is 12{~n}{:else}math result is not 12{~n}{/eq}
 {/math}
 
+
+Math with body: any{~n}
+==================={~n}
+{@math key="7" method="add" operand="4"}
+    {@eq value=10}math result is 10{~n}{:else}math result is not 10{~n}{/eq}
+    {@eq value=11}math result is 11{~n}{:else}math result is not 11{~n}{/eq}
+    {@eq value=12}math result is 12{~n}{:else}math result is not 12{~n}{/eq}
+    {@any}We found the value{~n}{/any}
+    {@none}We did not find the value{~n}{/none}
+{/math}
+
+Math with body: none{~n}
+===================={~n}
+{@math key="7" method="add" operand="4"}
+    {@eq value=10}math result is 10{~n}{:else}math result is not 10{~n}{/eq}
+    {@eq value=12}math result is 12{~n}{:else}math result is not 12{~n}{/eq}
+    {@any}We found the value{~n}{/any}
+    {@none}We did not find the value{~n}{/none}
+{/math}
+
+Math where method is a reference{~n}
+================================{~n}
+{@math key="7" method=add_operation operand="4" /}{~n}
+
+Math where method is a template{~n}
+==============================={~n}
+{@math key="7" method="{a_operation}dd" operand="4" /}{~n}
+
+Math where key is a template{~n}
+============================{~n}
+{@math key="{string_7}1" method="add" operand="4" /}{~n}
+
+Math where method is absent{~n}
+============================{~n}
+{@math key="7" operand="4" /}{~n}
+
+Math where method is missing{~n}
+============================{~n}
+{@math key="7" method=foobar operand="4" /}{~n}
+
+Math with unknown method{~n}
+========================{~n}
+{@math key="7" method="twirl" operand="4" /}{~n}
+
+Math with body where method is absent{~n}
+===================================={~n}
+{@math key="7" operand="4"}
+    {@eq value=12}math result is 12{~n}{:else}math result is not 12{~n}{/eq}
+    {@any}We found the value{~n}{/any}
+    {@none}We did not find the value{~n}{/none}
+    plain text not inside a tag{~n}
+{/math}

src/renderer/renderer.rs

@@ -644,7 +644,32 @@ impl<'a> DustRenderer<'a> {
                 }
                 _ => return Ok("".to_owned()),
             },
-            DustTag::DTHelperMath(parameterized_block) => {}
+            DustTag::DTHelperMath(parameterized_block) => {
+                let new_breadcrumbs = self.new_breadcrumbs_partial(
+                    breadcrumbs,
+                    breadcrumbs,
+                    None,
+                    &parameterized_block.explicit_context,
+                );
+                let new_breadcrumbs_ref = new_breadcrumbs.as_ref().unwrap_or(breadcrumbs);
+                let param_map =
+                    ParametersContext::new(self, breadcrumbs, &parameterized_block.params, None);
+                match &parameterized_block.contents {
+                    None => {
+                        // TODO: math without body, calculate the value and render it
+                        // Calculate the value
+                        // Render
+                    }
+                    Some(_) => {
+                        // TODO: math with body, calculate the value and use it like a select block
+                        // Calculate the value
+                        // Generate a ParametersContext with the result of the math operation as key
+                        // calculate are_any_checks_true
+                        // Generate a SelectContext
+                        // render_maybe_body
+                    }
+                }
+            }
         }
 
         Ok("".to_owned())
@@ -902,6 +927,52 @@ impl<'a> DustRenderer<'a> {
             _ => panic!("perform_comparison_check only implemented for comparison helpers (eq, ne, gt, gte, lt, lte)")
         }
     }
+
+    /// Performs a math operation (add, subtract, multiply, divide,
+    /// mod, abs, floor, ceil) and returns the result or None if
+    /// nothing should be rendered.
+    fn performance_math_operation(
+        &'a self,
+        breadcrumbs: &'a Vec<BreadcrumbTreeElement<'a>>,
+        math_parameters: &'a ParametersContext<'a>,
+    ) -> Option<IceResult<'a>> {
+        let method = match self.tap(breadcrumbs, math_parameters, "method") {
+            None | Some(Err(_)) => return None,
+            Some(Ok(ice_result)) => ice_result,
+        };
+        let method_rendered = match method.get_context_element_reference().render(&Vec::new()) {
+            Ok(text) => text,
+            Err(_) => return None,
+        };
+
+        let left_side = self.tap(breadcrumbs, math_parameters, "key");
+        let right_side = self.tap(breadcrumbs, math_parameters, "operand");
+
+        let left_side_ce = left_side.as_ref().map(|maybe_ice| {
+            maybe_ice
+                .as_ref()
+                .map(|ice| ice.get_context_element_reference())
+        });
+        let right_side_ce = right_side.as_ref().map(|maybe_ice| {
+            maybe_ice
+                .as_ref()
+                .map(|ice| ice.get_context_element_reference())
+        });
+
+        match method_rendered.as_str() {
+            "add" => todo!(),
+            "subtract" => todo!(),
+            "multiply" => todo!(),
+            "divide" => todo!(),
+            "mod" => todo!(),
+            "abs" => todo!(),
+            "floor" => todo!(),
+            "ceil" => todo!(),
+            _ => return None,
+        }
+
+        todo!()
+    }
 }
 
 struct BlockContext<'a> {