Implement .def/.defined expressions

This can be combined with .if/.elsif statements just like any other
expression.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

3 files changed, 57 insertions, 0 deletions

diff --git a/lib/xixanta/src/assembler.rs b/lib/xixanta/src/assembler.rs
index ce34983..d0a0e6e 100644
--- a/lib/xixanta/src/assembler.rs
+++ b/lib/xixanta/src/assembler.rs
@@ -1550,6 +1550,7 @@ impl<'a> Assembler<'a> {
         match node.node_type {
             NodeType::Control(ControlType::Hibyte) => self.evaluate_byte(node, true),
             NodeType::Control(ControlType::Lobyte) => self.evaluate_byte(node, false),
+            NodeType::Control(ControlType::Defined) => self.evaluate_defined(node),
             _ => Err(Error {
                 line: node.value.line,
                 message: format!(
@@ -1585,6 +1586,24 @@ impl<'a> Assembler<'a> {
         Ok(bundle)
     }
 
+    // Returns a bundle containing a boolean value on whether the symbol
+    // referenced in the given `node` is actually defined on this context or
+    // not.
+    fn evaluate_defined(&mut self, node: &PNode) -> Result<Bundle, Error> {
+        // Guaranteed by the parser to be only one argument.
+        let name = node.args.as_ref().unwrap().first().unwrap();
+
+        if self
+            .context
+            .get_variable(&name.value, &self.mappings)
+            .is_ok()
+        {
+            Ok(Bundle::fill(0x01))
+        } else {
+            Ok(Bundle::fill(0x00))
+        }
+    }
+
     fn push_evaluated_arguments(&mut self, node: &PNode, nbytes: u8) -> Result<(), Error> {
         match &node.args {
             Some(args) => {
@@ -3372,6 +3391,40 @@ jsr Movement::update
         );
     }
 
+    #[test]
+    fn defined() {
+        let res = just_bundles(
+            r#"Var = 0
+.if .defined(Var)
+  lda #1
+.else
+  lda #0
+.endif
+
+.if .defined(Var1)
+  lda #1
+.else
+  lda #0
+.endif
+
+.if !.defined(Var1)
+  lda #1
+.else
+  lda #0
+.endif
+"#,
+        );
+
+        assert_eq!(res.len(), 3);
+
+        let instrs: Vec<[u8; 2]> = vec![[0xA9, 0x01], [0xA9, 0x00], [0xA9, 0x01]];
+        for i in 0..instrs.len() {
+            assert_eq!(res[i].size, 2);
+            assert_eq!(res[i].bytes[0], instrs[i][0]);
+            assert_eq!(res[i].bytes[1], instrs[i][1]);
+        }
+    }
+
     // Macros
 
     #[test]
diff --git a/lib/xixanta/src/node.rs b/lib/xixanta/src/node.rs
index ae79f1e..f1eb558 100644
--- a/lib/xixanta/src/node.rs
+++ b/lib/xixanta/src/node.rs
@@ -147,6 +147,7 @@ pub enum ControlType {
     Elsif,
     Else,
     EndIf,
+    Defined,
 }
 
 impl fmt::Display for ControlType {
@@ -174,6 +175,7 @@ impl fmt::Display for ControlType {
             ControlType::Elsif => write!(f, ".elsif"),
             ControlType::Else => write!(f, ".else"),
             ControlType::EndIf => write!(f, ".endif"),
+            ControlType::Defined => write!(f, ".defined"),
         }
     }
 }
diff --git a/lib/xixanta/src/opcodes.rs b/lib/xixanta/src/opcodes.rs
index 8488b77..80878ec 100644
--- a/lib/xixanta/src/opcodes.rs
+++ b/lib/xixanta/src/opcodes.rs
@@ -761,6 +761,8 @@ lazy_static! {
         functions.insert(String::from(".elsif"), Control { control_type: ControlType::Elsif, has_identifier: None, required_args: Some((1, 1)), touches_context: false, only_string: false });
         functions.insert(String::from(".else"), Control { control_type: ControlType::Else, has_identifier: None, required_args: Some((0, 0)), touches_context: false, only_string: false });
         functions.insert(String::from(".endif"), Control { control_type: ControlType::EndIf, has_identifier: None, required_args: Some((0, 0)), touches_context: false, only_string: false });
+        functions.insert(String::from(".def"), Control { control_type: ControlType::Defined, has_identifier: None, required_args: Some((1, 1)), touches_context: false, only_string: false });
+        functions.insert(String::from(".defined"), Control { control_type: ControlType::Defined, has_identifier: None, required_args: Some((1, 1)), touches_context: false, only_string: false });
 
         functions
     };