Begin implementing built-in functions

src/value.rs

@@ -13,8 +13,9 @@ use stanza::{
 };
 
 use crate::{
-    abstract_tree::{Identifier, Statement, Type},
-    error::ValidationError,
+    abstract_tree::{Action, Identifier, Statement, Type},
+    context::Context,
+    error::{RuntimeError, ValidationError},
 };
 
 pub static NONE: OnceLock<Value> = OnceLock::new();
@@ -77,11 +78,13 @@ impl Value {
         return_type: Type,
         body: Statement,
     ) -> Self {
-        Value(Arc::new(ValueInner::Function(Function {
+        Value(Arc::new(ValueInner::Function(Function::Parsed(
+            ParsedFunction {
                 parameters,
                 return_type,
                 body,
-        })))
+            },
+        ))))
     }
 
     pub fn r#type(&self) -> Type {
@@ -227,11 +230,11 @@ impl Display for Value {
             ValueInner::String(string) => write!(f, "{string}"),
 
             ValueInner::Enum(_, _) => todo!(),
-            ValueInner::Function(Function {
+            ValueInner::Function(Function::Parsed(ParsedFunction {
                 parameters,
                 return_type,
                 body,
-            }) => {
+            })) => {
                 write!(f, "(")?;
 
                 for (identifier, r#type) in parameters {
@@ -240,6 +243,9 @@ impl Display for Value {
 
                 write!(f, "): {return_type} {body:?}")
             }
+            ValueInner::Function(Function::BuiltIn(built_in_function)) => {
+                write!(f, "{built_in_function}")
+            }
         }
     }
 }
@@ -323,8 +329,48 @@ impl Ord for ValueInner {
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
-pub struct Function {
+pub enum Function {
+    Parsed(ParsedFunction),
+    BuiltIn(BuiltInFunction),
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
+pub struct ParsedFunction {
     parameters: Vec<(Identifier, Type)>,
     return_type: Type,
     body: Statement,
 }
+
+#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
+pub enum BuiltInFunction {
+    Output(Value),
+}
+
+impl BuiltInFunction {
+    fn r#type(&self, context: &Context) -> Type {
+        match self {
+            BuiltInFunction::Output(_) => Type::Function {
+                parameter_types: vec![Type::Any],
+                return_type: Box::new(Type::None),
+            },
+        }
+    }
+
+    fn call(self, context: &Context) -> Result<Action, RuntimeError> {
+        match self {
+            BuiltInFunction::Output(value) => {
+                println!("{value}");
+
+                Ok(Action::None)
+            }
+        }
+    }
+}
+
+impl Display for BuiltInFunction {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            BuiltInFunction::Output(_) => write!(f, "(to_output : any) : none rust_magic();"),
+        }
+    }
+}

tests/functions.rs

@@ -0,0 +1,115 @@
+use dust_lang::{
+    abstract_tree::Identifier,
+    error::{Error, ValidationError},
+    *,
+};
+
+#[test]
+fn function_call() {
+    assert_eq!(
+        interpret(
+            "
+            foobar = (message : str) : str { message }
+            foobar('Hiya')
+            ",
+        ),
+        Ok(Some(Value::string("Hiya".to_string())))
+    );
+}
+
+#[test]
+fn call_empty_function() {
+    assert_eq!(
+        interpret(
+            "
+            foobar = (message : str) : none {}
+            foobar('Hiya')
+            ",
+        ),
+        Ok(None)
+    );
+}
+
+#[test]
+fn callback() {
+    assert_eq!(
+        interpret(
+            "
+            foobar = (cb : () -> str) : str {
+                cb()
+            }
+            foobar(() : str { 'Hiya' })
+            ",
+        ),
+        Ok(Some(Value::string("Hiya".to_string())))
+    );
+}
+
+#[test]
+fn built_in_function_call() {
+    assert_eq!(interpret("output('Hiya')"), Ok(None));
+}
+
+#[test]
+fn function_context_does_not_capture_values() {
+    assert_eq!(
+        interpret(
+            "
+            x = 1
+
+            foo = () : any { x }
+            "
+        ),
+        Err(vec![Error::Validation {
+            error: ValidationError::VariableNotFound(Identifier::new("x")),
+            span: (0..0).into()
+        }])
+    );
+
+    assert_eq!(
+        interpret(
+            "
+            x = 1
+            foo = (x : int) : int { x }
+            foo(2)
+            "
+        ),
+        Ok(Some(Value::integer(2)))
+    );
+}
+
+#[test]
+fn function_context_captures_functions() {
+    assert_eq!(
+        interpret(
+            "
+            bar = () : int { 2 }
+            foo = () : int { bar() }
+            foo()
+            "
+        ),
+        Ok(Some(Value::integer(2)))
+    );
+}
+
+#[test]
+fn recursion() {
+    env_logger::builder().is_test(true).try_init().unwrap();
+
+    assert_eq!(
+        interpret(
+            "
+            fib = (i : int) : int {
+            	if i <= 1 {
+            		1
+            	} else {
+            		fib(i - 1) + fib(i - 2)
+            	}
+            }
+
+            fib(8)
+            "
+        ),
+        Ok(Some(Value::integer(34)))
+    );
+}