Implemented greatest and least.

Author: kennytm

Template.md

@@ -233,8 +233,14 @@ From highest to lowest precedence:
 
     If *value* equals to *p1*, then the expression's value is *r1*, etc.
 
-* **@local := f()**
-
 * **@local**
 
     Gets the previous assigned local variable. If the variable was undefined, this will return NULL.
+
+* **greatest(*x*, *y*, *z*)**
+
+    Returns the largest of all given values. NULL values are ignored.
+
+* **least(*x*, *y*, *z*)**
+
+    Returns the smallest of all given values. NULL values are ignored.

src/eval.rs

@@ -405,5 +405,22 @@ pub fn compile_function(name: Function, args: &[impl AsValue]) -> Result<Compile
                 Compiled(C::Constant(Value::Null))
             })
         }
+
+        Function::Greatest | Function::Least => {
+            let mut res = &Value::Null;
+            for value in iter_args::<&Value, _>(name, args) {
+                let value = value?;
+                let should_replace = match value.sql_cmp(res, name)? {
+                    Some(Ordering::Greater) => name == Function::Greatest,
+                    Some(Ordering::Less) => name == Function::Least,
+                    None => res == &Value::Null,
+                    _ => false
+                };
+                if should_replace {
+                    res = value;
+                }
+            }
+            Ok(Compiled(C::Constant(res.clone())))
+        }
     }
 }

src/parser.rs

@@ -403,6 +403,9 @@ define_function! {
         RandLogNormal = "rand.log_normal",
         RandBool = "rand.bool",
 
+        Greatest = "greatest",
+        Least = "least",
+
     'sym_op:
         Eq = "=",
         Lt = "<",