Add if() function

src/builtin/color.rs

@@ -2,27 +2,7 @@ use std::collections::BTreeMap;
 
 use super::Builtin;
 use crate::value::Value;
-
-macro_rules! arg {
-    ($args:ident, $idx:literal, $name:literal) => {
-        match $args.get(stringify!($idx)) {
-            Some(v) => v,
-            None => match $args.get($name) {
-                Some(v) => v,
-                None => panic!("missing variable"),
-            },
-        };
-    };
-    ($args:ident, $idx:literal, $name:literal, $default:literal) => {
-        match $args.get(stringify!($idx)) {
-            Some(v) => v,
-            None => match $args.get($name) {
-                Some(v) => v,
-                None => $default,
-            },
-        };
-    };
-}
+use crate::color::Color;
 
 pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
     f.insert(
@@ -33,7 +13,7 @@ pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
                 let _red: &Value = arg!(args, 0, "red");
                 let _green: &Value = arg!(args, 1, "green");
                 let _blue: &Value = arg!(args, 2, "blue");
-            // Value::Color()
+            // Value::Color(Color::RGB(red, blue, green))
             } else {
                 todo!("channels variable in `rgb`")
             };

src/builtin/meta.rs

@@ -1 +1,20 @@
+use std::collections::BTreeMap;
 
+use super::Builtin;
+use crate::value::Value;
+
+pub(crate) fn register(f: &mut BTreeMap<String, Builtin>) {
+    f.insert(
+        "if".to_owned(),
+        Box::new(|args| {
+            let cond: &Value = arg!(args, 0, "condition");
+            let if_true = arg!(args, 1, "if-true").clone();
+            let if_false = arg!(args, 2, "if-false").clone();
+            if cond.is_true() {
+                Some(if_true)
+            } else {
+                Some(if_false)
+            }
+        }),
+    );
+}

src/builtin/mod.rs

@@ -4,6 +4,28 @@ use std::collections::BTreeMap;
 use crate::args::CallArgs;
 use crate::value::Value;
 
+macro_rules! arg {
+    ($args:ident, $idx:literal, $name:literal) => {
+        match $args.get(stringify!($idx)) {
+            Some(v) => v,
+            None => match $args.get($name) {
+                Some(v) => v,
+                None => panic!("missing variable"),
+            },
+        };
+    };
+    ($args:ident, $idx:literal, $name:literal, $default:literal) => {
+        match $args.get(stringify!($idx)) {
+            Some(v) => v,
+            None => match $args.get($name) {
+                Some(v) => v,
+                None => $default,
+            },
+        };
+    };
+}
+
+
 mod color;
 mod list;
 mod map;
@@ -18,6 +40,7 @@ lazy_static! {
     pub(crate) static ref GLOBAL_FUNCTIONS: BTreeMap<String, Builtin> = {
         let mut m = BTreeMap::new();
         color::register(&mut m);
+        meta::register(&mut m);
         m
     };
 }

src/value.rs

@@ -217,7 +217,7 @@ impl Value {
     }
 
     pub fn is_true(&self) -> bool {
-        todo!()
+        !(self == &Value::Null || self == &Value::False)
     }
 
     pub fn unquote(self) -> Self {