Merge pull request #64 from FredTheDino/constants

constants

2 files changed, 69 insertions, 1 deletions

diff --git a/src/compiler.rs b/src/compiler.rs
index 128b4a8..eb6058a 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -126,6 +126,7 @@ struct Variable {
     active: bool,
     upvalue: bool,
     captured: bool,
+    mutable: bool,
 }
 
 struct Frame {
@@ -798,6 +799,32 @@ impl Compiler {
             scope,
             active: false,
             upvalue: false,
+            mutable: true,
+        });
+        Ok(slot)
+    }
+
+    fn define_constant(&mut self, name: &str, typ: Type, _block: &mut Block) -> Result<usize, ()> {
+        if let Some(var) = self.find_variable(&name) {
+            if var.scope == self.frame().scope {
+                error!(self, format!("Multiple definitions of {} in this block.", name));
+                return Err(());
+            }
+        }
+
+        let slot = self.stack().len();
+        let scope = self.frame().scope;
+        self.stack_mut().push(Variable {
+            name: String::from(name),
+            captured: false,
+            outer_upvalue: false,
+            outer_slot: 0,
+            slot,
+            typ,
+            scope,
+            active: false,
+            upvalue: false,
+            mutable: false,
         });
         Ok(slot)
     }
@@ -813,6 +840,15 @@ impl Compiler {
         }
     }
 
+    fn constant_statement(&mut self, name: &str, typ: Type, block: &mut Block) {
+        let slot = self.define_constant(name, typ.clone(), block);
+        self.expression(block);
+
+        if let Ok(slot) = slot {
+            self.stack_mut()[slot].active = true;
+        }
+    }
+
     fn assign(&mut self, block: &mut Block) {
         let name = match self.eat() {
             Token::Identifier(name) => name,
@@ -837,6 +873,10 @@ impl Compiler {
         };
 
         if let Some(var) = self.find_variable(&name) {
+            if !var.mutable {
+                // TODO(ed): Maybe a better error than "SyntaxError".
+                error!(self, format!("Cannot assign to constant '{}'", var.name));
+            }
             if let Some(op) = op {
                 if var.upvalue {
                     add_op(self, block, Op::ReadUpvalue(var.slot));
@@ -1165,6 +1205,12 @@ impl Compiler {
                 self.definition_statement(&name, Type::Unknown, block);
             }
 
+            (Token::Identifier(name), Token::ColonColon, ..) => {
+                self.eat();
+                self.eat();
+                self.constant_statement(&name, Type::Unknown, block);
+            }
+
             (Token::Blob, Token::Identifier(_), ..) => {
                 self.blob_statement(block);
             }
@@ -1219,6 +1265,7 @@ impl Compiler {
             active: false,
             captured: false,
             upvalue: false,
+            mutable: true,
         });
 
         let mut block = Block::new(name, file, 0);
diff --git a/src/lib.rs b/src/lib.rs
index 862e9fa..22b6713 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -805,6 +805,16 @@ mod tests {
         assert_errs!(run_string("<!>\n", true, Vec::new()), [ErrorKind::Unreachable]);
     }
 
+    #[test]
+    fn assign_to_constant() {
+        assert_errs!(run_string("a :: 2\na = 2", true, Vec::new()), [ErrorKind::SyntaxError(_, _)]);
+    }
+
+    #[test]
+    fn assign_to_constant_upvalue() {
+        assert_errs!(run_string("a :: 2\nq :: fn { a = 2 }\n", true, Vec::new()), [ErrorKind::SyntaxError(_, _)]);
+    }
+
     macro_rules! test_multiple {
         ($mod:ident, $( $fn:ident : $prog:literal ),+ $( , )? ) => {
             mod $mod {
@@ -848,7 +858,7 @@ mod tests {
     test_multiple!(
         if_,
         compare_constants_equality: "if 1 == 2 {
-                                       <!>
+                                        <!>
                                      }",
         compare_constants_unequality: "if 1 != 1 {
                                          <!>
@@ -1060,6 +1070,17 @@ a.a <=> 0"
     );
 
     test_multiple!(
+        read_constants,
+        simple: "
+a :: 1
+a <=> 1
+b := 2
+{
+    a <=> 1
+}",
+    );
+
+    test_multiple!(
         assignment_op_regression,
         simple_add: "
 a := 0