diff --git a/src/ast.rs b/src/ast.rs
index 00b3a24..2abcea8 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -16,3 +16,47 @@ pub struct ConstantDef<'a> {
     pub ident: &'a str,
     pub value: Constant<'a>,
 }
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SimpleType {
+    Integer,
+    Real,
+    Boolean,
+    Char,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum RecordField<'input> {
+    Fixed {
+        identifier_list: Vec<&'input str>,
+        type_denoter: Type<'input>,
+    },
+    Case {
+        // TODO: 6.4.3.3 Record-types
+    },
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Type<'input> {
+    Identifier(&'input str),
+    Simple(SimpleType),
+    Enumerated(Vec<&'input str>),
+    Subrange {
+        start: Constant<'input>,
+        end: Constant<'input>,
+    },
+    Array {
+        index: Vec<Type<'input>>,
+        component: Box<Type<'input>>,
+        packed: bool,
+    },
+    Record {
+        fields: Vec<RecordField<'input>>,
+    },
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TypeDef<'input> {
+    pub ident: &'input str,
+    pub value: Type<'input>,
+}
diff --git a/src/grammar.lalrpop b/src/grammar.lalrpop
index 016a58c..9e2b498 100644
--- a/src/grammar.lalrpop
+++ b/src/grammar.lalrpop
@@ -18,6 +18,7 @@ extern {
         "string" => Token::String(<&'input str>),
         "-" => Token::SpecialMinus,
         "+" => Token::SpecialPlus,
+        "=" => Token::SpecialEqual,
     }
 }
 
@@ -42,3 +43,10 @@ pub Constant: ast::Constant<'input> = {
     "+"? <ident:"identifier"> => ast::Constant::Identifier { is_negative: false, ident },
     "-" <ident:"identifier"> => ast::Constant::Identifier { is_negative: true, ident },
 }
+
+pub ConstantDef: ast::ConstantDef<'input> = {
+    <ident:"identifier"> "=" <value:Constant> => ast::ConstantDef {
+        ident,
+        value
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 36ade0a..318f92d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -66,8 +66,28 @@ mod test {
         check("2.2", ast::Constant::Number(ast::Number::Real("2.2")));
         check("1e10", ast::Constant::Number(ast::Number::Real("1e10")));
 
-
         check(r#""hello world""#, ast::Constant::String("\"hello world\""));
-        check(r#""\"hell\"o world""#, ast::Constant::String("\"\\\"hell\\\"o world\""));
+        check(
+            r#""\"hell\"o world""#,
+            ast::Constant::String("\"\\\"hell\\\"o world\""),
+        );
+    }
+
+    #[test]
+    fn parse_constant_definition() {
+        #[track_caller]
+        fn check(input: &str, value: ast::ConstantDef) {
+            let lexer = Lexer::new(input);
+            let parser = grammar::ConstantDefParser::new();
+            assert_eq!(parser.parse("", lexer).unwrap(), value)
+        }
+
+        check(
+            "MYIDENTIFIER = 2.2",
+            ast::ConstantDef {
+                ident: "MYIDENTIFIER",
+                value: ast::Constant::Number(ast::Number::Real("2.2")),
+            },
+        );
     }
 }