diff --git a/core/ast/json_serializer.py b/core/ast/json_serializer.py
index 0c3d773..0064726 100644
--- a/core/ast/json_serializer.py
+++ b/core/ast/json_serializer.py
@@ -1,14 +1,24 @@
+from typing import Optional, Sequence
+
 from core.ast.midas import (
-    ConstraintExpr,
-    ConstraintStmt,
+    BinaryExpr,
+    ComplexTypeStmt,
     Expr,
+    ExtendStmt,
+    GetExpr,
+    GroupingExpr,
     LiteralExpr,
+    LogicalExpr,
     OpStmt,
+    PredicateStmt,
     PropertyStmt,
+    SimpleTypeExpr,
+    SimpleTypeStmt,
     Stmt,
-    TypeBodyExpr,
+    TemplateExpr,
     TypeExpr,
-    TypeStmt,
+    UnaryExpr,
+    VariableExpr,
     WildcardExpr,
 )
 
@@ -19,42 +29,29 @@ class AstJsonSerializer(Stmt.Visitor[dict], Expr.Visitor[dict]):
     def serialize(self, stmts: list[Stmt]) -> list[dict]:
         return [stmt.accept(self) for stmt in stmts]
 
-    def visit_type_stmt(self, stmt: TypeStmt) -> dict:
+    def _serialize_optional(self, element: Optional[Stmt | Expr]) -> Optional[dict]:
+        if element is None:
+            return None
+        return element.accept(self)
+
+    def _serialize_list(self, elements: Sequence[Stmt | Expr]) -> list[dict]:
+        return [element.accept(self) for element in elements]
+
+    def visit_simple_type_stmt(self, stmt: SimpleTypeStmt) -> dict:
         return {
-            "_type": "TypeStmt",
+            "_type": "SimpleTypeStmt",
+            "template": self._serialize_optional(stmt.template),
             "name": stmt.name.lexeme,
-            "bases": [base.accept(self) for base in stmt.bases],
-            "body": stmt.body.accept(self) if stmt.body is not None else None,
+            "base": stmt.base.accept(self),
+            "constraint": self._serialize_optional(stmt.constraint),
         }
 
-    def visit_type_expr(self, expr: TypeExpr) -> dict:
+    def visit_complex_type_stmt(self, stmt: ComplexTypeStmt) -> dict:
         return {
-            "_type": "TypeExpr",
-            "name": expr.name.lexeme,
-            "constraints": [constraint.accept(self) for constraint in expr.constraints],
-        }
-
-    def visit_constraint_expr(self, expr: ConstraintExpr) -> dict:
-        return {
-            "_type": "ConstraintExpr",
-            "left": expr.left.accept(self),
-            "op": expr.op.lexeme,
-            "right": expr.right.accept(self),
-        }
-
-    def visit_wildcard_expr(self, expr: WildcardExpr) -> dict:
-        return {"_type": "WildcardExpr"}
-
-    def visit_literal_expr(self, expr: LiteralExpr) -> dict:
-        return {
-            "_type": "LiteralExpr",
-            "value": expr.value,
-        }
-
-    def visit_type_body_expr(self, expr: TypeBodyExpr) -> dict:
-        return {
-            "_type": "TypeBodyExpr",
-            "properties": [prop.accept(self) for prop in expr.properties],
+            "_type": "ComplexTypeStmt",
+            "name": stmt.name.lexeme,
+            "template": self._serialize_optional(stmt.template),
+            "properties": self._serialize_list(stmt.properties),
         }
 
     def visit_property_stmt(self, stmt: PropertyStmt) -> dict:
@@ -62,20 +59,101 @@ class AstJsonSerializer(Stmt.Visitor[dict], Expr.Visitor[dict]):
             "_type": "PropertyStmt",
             "name": stmt.name.lexeme,
             "type": stmt.type.accept(self),
+            "constraint": self._serialize_optional(stmt.constraint),
+        }
+
+    def visit_extend_stmt(self, stmt: ExtendStmt) -> dict:
+        return {
+            "_type": "ExtendStmt",
+            "type": stmt.type.accept(self),
+            "operations": self._serialize_list(stmt.operations),
         }
 
     def visit_op_stmt(self, stmt: OpStmt) -> dict:
         return {
             "_type": "OpStmt",
-            "left": stmt.left.accept(self),
-            "op": stmt.op.lexeme,
-            "right": stmt.right.accept(self),
+            "name": stmt.name.lexeme,
+            "operand": stmt.operand.accept(self),
             "result": stmt.result.accept(self),
         }
 
-    def visit_constraint_stmt(self, stmt: ConstraintStmt) -> dict:
+    def visit_predicate_stmt(self, stmt: PredicateStmt) -> dict:
         return {
-            "_type": "ConstraintStmt",
+            "_type": "PredicateStmt",
             "name": stmt.name.lexeme,
-            "constraint": stmt.constraint.accept(self),
+            "subject": stmt.subject.lexeme,
+            "type": stmt.type.accept(self),
+            "condition": stmt.condition.accept(self),
+        }
+
+    def visit_simple_type_expr(self, expr: SimpleTypeExpr) -> dict:
+        return {
+            "_type": "SimpleTypeExpr",
+            "name": expr.name.lexeme,
+            "optional": expr.optional,
+        }
+
+    def visit_logical_expr(self, expr: LogicalExpr) -> dict:
+        return {
+            "_type": "LogicalExpr",
+            "left": expr.left.accept(self),
+            "operator": expr.operator.lexeme,
+            "right": expr.right.accept(self),
+        }
+
+    def visit_binary_expr(self, expr: BinaryExpr) -> dict:
+        return {
+            "_type": "BinaryExpr",
+            "left": expr.left.accept(self),
+            "operator": expr.operator.lexeme,
+            "right": expr.right.accept(self),
+        }
+
+    def visit_unary_expr(self, expr: UnaryExpr) -> dict:
+        return {
+            "_type": "UnaryExpr",
+            "operator": expr.operator.lexeme,
+            "right": expr.right.accept(self),
+        }
+
+    def visit_get_expr(self, expr: GetExpr) -> dict:
+        return {
+            "_type": "GetExpr",
+            "expr": expr.expr.accept(self),
+            "name": expr.name.lexeme,
+        }
+
+    def visit_variable_expr(self, expr: VariableExpr) -> dict:
+        return {
+            "_type": "VariableExpr",
+            "name": expr.name.lexeme,
+        }
+
+    def visit_grouping_expr(self, expr: GroupingExpr) -> dict:
+        return {
+            "_type": "GroupingExpr",
+            "expr": expr.expr.accept(self),
+        }
+
+    def visit_literal_expr(self, expr: LiteralExpr) -> dict:
+        return {
+            "_type": "LiteralExpr",
+            "value": expr.value,
+        }
+
+    def visit_wildcard_expr(self, expr: WildcardExpr) -> dict:
+        return {"_type": "WildcardExpr"}
+
+    def visit_template_expr(self, expr: TemplateExpr) -> dict:
+        return {
+            "_type": "TemplateExpr",
+            "type": expr.type.accept(self),
+        }
+
+    def visit_type_expr(self, expr: TypeExpr) -> dict:
+        return {
+            "_type": "TypeExpr",
+            "name": expr.name.lexeme,
+            "template": self._serialize_optional(expr.template),
+            "optional": expr.optional,
         }
diff --git a/tests/cases/parser/01_simple_types.midas b/tests/cases/parser/01_simple_types.midas
index 017e40c..9432751 100644
--- a/tests/cases/parser/01_simple_types.midas
+++ b/tests/cases/parser/01_simple_types.midas
@@ -1,24 +1,57 @@
-// Simple custom type derived from floats
-type Latitude<float>
-type Longitude<float>
+// Simple custom type derived from float
+type Custom(float)
+
+// Simple custom types with constraints
+type Latitude(float) where (-90 <= _ <= 90)
+type Longitude(float) where (-180 <= _ <= 180)
+
+// Generic custom type (a Difference of T is derived from T, e.g. a difference of floats is a float
+type Difference[T](T)
 
 // Complex custom type, containing two values accessible through properties
-type GeoLocation<Latitude, Longitude> {
+type GeoLocation {
     lat: Latitude
     lon: Longitude
 }
 
-type LatitudeDiff<float>
-type LongitudeDiff<float>
+// Define operations on our custom type
+extend GeoLocation {
+    // This type is compatible with the `-` operation with another GeoLocation
+    // i.e. you can subtract a GeoLocation from another GeoLocation, resulting
+    // in a Difference of GeoLocations
+    op __sub__(GeoLocation) -> Difference[GeoLocation]
+}
+
+// For complex generics, you need to specify how the genericity the properties
+// are handled
+type Difference[GeoLocation] {
+    lat: Difference[Latitude]
+    lon: Difference[Longitude]
+}
 
 // Simple operation defined on our custom types
-op <Latitude> - <Latitude> = <LatitudeDiff>
-op <Longitude> - <Longitude> = <LongitudeDiff>
+extend Latitude {
+    op __sub__(Latitude) -> Difference[Latitude]
+}
 
-// Simple custom type with a constraint
-type Age<int + (0 <= _) + (_ < 150)>
+extend Longitude {
+    op __sub__(Longitude) -> Difference[Longitude]
+}
 
-// Predefined custom constraints that can be referenced in other definitions
-constraint Positive = _ >= 0
-constraint StrictlyPositive = _ > 0
-//constraint Even = _ % 2 == 0
\ No newline at end of file
+// Predefined custom predicates that can be referenced in other definitions
+predicate Positive(v: float) = v >= 0
+predicate StrictlyPositive(v: float) = v > 0
+predicate Equatorial(loc: GeoLocation) = (-10 <= loc.lat <= 10)
+predicate Arctic(loc: GeoLocation) = (loc.lat >= 66)
+
+type Person {
+    name: str
+
+    // Property with an inline constraint
+    age: int? where (0 <= _ < 150)
+
+    // Property referencing a predicate
+    height: float where StrictlyPositive
+
+    home: GeoLocation
+}
diff --git a/tests/cases/parser/01_simple_types.midas.ref.json b/tests/cases/parser/01_simple_types.midas.ref.json
index 0697e32..9c9aa5b 100644
--- a/tests/cases/parser/01_simple_types.midas.ref.json
+++ b/tests/cases/parser/01_simple_types.midas.ref.json
@@ -2,7 +2,7 @@
   "tokens": [
     {
       "type": "COMMENT",
-      "lexeme": "// Simple custom type derived from floats",
+      "lexeme": "// Simple custom type derived from float",
       "line": 1,
       "column": 1
     },
@@ -10,7 +10,7 @@
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 1,
-      "column": 42
+      "column": 41
     },
     {
       "type": "TYPE",
@@ -26,93 +26,183 @@
     },
     {
       "type": "IDENTIFIER",
-      "lexeme": "Latitude",
+      "lexeme": "Custom",
       "line": 2,
       "column": 6
     },
     {
-      "type": "LESS",
-      "lexeme": "<",
+      "type": "LEFT_PAREN",
+      "lexeme": "(",
       "line": 2,
-      "column": 14
+      "column": 12
     },
     {
       "type": "IDENTIFIER",
       "lexeme": "float",
       "line": 2,
-      "column": 15
+      "column": 13
     },
     {
-      "type": "GREATER",
-      "lexeme": ">",
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
       "line": 2,
-      "column": 20
+      "column": 18
     },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 2,
-      "column": 21
+      "column": 19
     },
     {
-      "type": "TYPE",
-      "lexeme": "type",
+      "type": "NEWLINE",
+      "lexeme": "\n",
       "line": 3,
       "column": 1
     },
     {
-      "type": "WHITESPACE",
-      "lexeme": " ",
-      "line": 3,
-      "column": 5
-    },
-    {
-      "type": "IDENTIFIER",
-      "lexeme": "Longitude",
-      "line": 3,
-      "column": 6
-    },
-    {
-      "type": "LESS",
-      "lexeme": "<",
-      "line": 3,
-      "column": 15
-    },
-    {
-      "type": "IDENTIFIER",
-      "lexeme": "float",
-      "line": 3,
-      "column": 16
-    },
-    {
-      "type": "GREATER",
-      "lexeme": ">",
-      "line": 3,
-      "column": 21
-    },
-    {
-      "type": "NEWLINE",
-      "lexeme": "\n",
-      "line": 3,
-      "column": 22
+      "type": "COMMENT",
+      "lexeme": "// Simple custom types with constraints",
+      "line": 4,
+      "column": 1
     },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 4,
+      "column": 40
+    },
+    {
+      "type": "TYPE",
+      "lexeme": "type",
+      "line": 5,
       "column": 1
     },
     {
-      "type": "COMMENT",
-      "lexeme": "// Complex custom type, containing two values accessible through properties",
+      "type": "WHITESPACE",
+      "lexeme": " ",
       "line": 5,
-      "column": 1
+      "column": 5
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "Latitude",
+      "line": 5,
+      "column": 6
+    },
+    {
+      "type": "LEFT_PAREN",
+      "lexeme": "(",
+      "line": 5,
+      "column": 14
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "float",
+      "line": 5,
+      "column": 15
+    },
+    {
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
+      "line": 5,
+      "column": 20
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 5,
+      "column": 21
+    },
+    {
+      "type": "WHERE",
+      "lexeme": "where",
+      "line": 5,
+      "column": 22
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 5,
+      "column": 27
+    },
+    {
+      "type": "LEFT_PAREN",
+      "lexeme": "(",
+      "line": 5,
+      "column": 28
+    },
+    {
+      "type": "MINUS",
+      "lexeme": "-",
+      "line": 5,
+      "column": 29
+    },
+    {
+      "type": "NUMBER",
+      "lexeme": "90",
+      "line": 5,
+      "column": 30
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 5,
+      "column": 32
+    },
+    {
+      "type": "LESS_EQUAL",
+      "lexeme": "<=",
+      "line": 5,
+      "column": 33
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 5,
+      "column": 35
+    },
+    {
+      "type": "UNDERSCORE",
+      "lexeme": "_",
+      "line": 5,
+      "column": 36
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 5,
+      "column": 37
+    },
+    {
+      "type": "LESS_EQUAL",
+      "lexeme": "<=",
+      "line": 5,
+      "column": 38
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 5,
+      "column": 40
+    },
+    {
+      "type": "NUMBER",
+      "lexeme": "90",
+      "line": 5,
+      "column": 41
+    },
+    {
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
+      "line": 5,
+      "column": 43
     },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 5,
-      "column": 76
+      "column": 44
     },
     {
       "type": "TYPE",
@@ -128,147 +218,201 @@
     },
     {
       "type": "IDENTIFIER",
-      "lexeme": "GeoLocation",
+      "lexeme": "Longitude",
       "line": 6,
       "column": 6
     },
     {
-      "type": "LESS",
-      "lexeme": "<",
+      "type": "LEFT_PAREN",
+      "lexeme": "(",
       "line": 6,
-      "column": 17
+      "column": 15
     },
     {
       "type": "IDENTIFIER",
-      "lexeme": "Latitude",
+      "lexeme": "float",
       "line": 6,
-      "column": 18
+      "column": 16
     },
     {
-      "type": "COMMA",
-      "lexeme": ",",
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
       "line": 6,
-      "column": 26
+      "column": 21
     },
     {
       "type": "WHITESPACE",
       "lexeme": " ",
       "line": 6,
-      "column": 27
+      "column": 22
     },
     {
-      "type": "IDENTIFIER",
-      "lexeme": "Longitude",
+      "type": "WHERE",
+      "lexeme": "where",
+      "line": 6,
+      "column": 23
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
       "line": 6,
       "column": 28
     },
     {
-      "type": "GREATER",
-      "lexeme": ">",
+      "type": "LEFT_PAREN",
+      "lexeme": "(",
       "line": 6,
-      "column": 37
+      "column": 29
+    },
+    {
+      "type": "MINUS",
+      "lexeme": "-",
+      "line": 6,
+      "column": 30
+    },
+    {
+      "type": "NUMBER",
+      "lexeme": "180",
+      "line": 6,
+      "column": 31
     },
     {
       "type": "WHITESPACE",
       "lexeme": " ",
       "line": 6,
+      "column": 34
+    },
+    {
+      "type": "LESS_EQUAL",
+      "lexeme": "<=",
+      "line": 6,
+      "column": 35
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 6,
+      "column": 37
+    },
+    {
+      "type": "UNDERSCORE",
+      "lexeme": "_",
+      "line": 6,
       "column": 38
     },
     {
-      "type": "LEFT_BRACE",
-      "lexeme": "{",
+      "type": "WHITESPACE",
+      "lexeme": " ",
       "line": 6,
       "column": 39
     },
     {
-      "type": "NEWLINE",
-      "lexeme": "\n",
+      "type": "LESS_EQUAL",
+      "lexeme": "<=",
       "line": 6,
       "column": 40
     },
-    {
-      "type": "WHITESPACE",
-      "lexeme": "    ",
-      "line": 7,
-      "column": 1
-    },
-    {
-      "type": "IDENTIFIER",
-      "lexeme": "lat",
-      "line": 7,
-      "column": 5
-    },
-    {
-      "type": "COLON",
-      "lexeme": ":",
-      "line": 7,
-      "column": 8
-    },
     {
       "type": "WHITESPACE",
       "lexeme": " ",
-      "line": 7,
-      "column": 9
+      "line": 6,
+      "column": 42
     },
     {
-      "type": "IDENTIFIER",
-      "lexeme": "Latitude",
-      "line": 7,
-      "column": 10
+      "type": "NUMBER",
+      "lexeme": "180",
+      "line": 6,
+      "column": 43
+    },
+    {
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
+      "line": 6,
+      "column": 46
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 6,
+      "column": 47
     },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 7,
+      "column": 1
+    },
+    {
+      "type": "COMMENT",
+      "lexeme": "// Generic custom type (a Difference of T is derived from T, e.g. a difference of floats is a float",
+      "line": 8,
+      "column": 1
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 8,
+      "column": 100
+    },
+    {
+      "type": "TYPE",
+      "lexeme": "type",
+      "line": 9,
+      "column": 1
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 9,
+      "column": 5
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "Difference",
+      "line": 9,
+      "column": 6
+    },
+    {
+      "type": "LEFT_BRACKET",
+      "lexeme": "[",
+      "line": 9,
+      "column": 16
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "T",
+      "line": 9,
+      "column": 17
+    },
+    {
+      "type": "RIGHT_BRACKET",
+      "lexeme": "]",
+      "line": 9,
       "column": 18
     },
     {
-      "type": "WHITESPACE",
-      "lexeme": "    ",
-      "line": 8,
-      "column": 1
-    },
-    {
-      "type": "IDENTIFIER",
-      "lexeme": "lon",
-      "line": 8,
-      "column": 5
-    },
-    {
-      "type": "COLON",
-      "lexeme": ":",
-      "line": 8,
-      "column": 8
-    },
-    {
-      "type": "WHITESPACE",
-      "lexeme": " ",
-      "line": 8,
-      "column": 9
-    },
-    {
-      "type": "IDENTIFIER",
-      "lexeme": "Longitude",
-      "line": 8,
-      "column": 10
-    },
-    {
-      "type": "NEWLINE",
-      "lexeme": "\n",
-      "line": 8,
+      "type": "LEFT_PAREN",
+      "lexeme": "(",
+      "line": 9,
       "column": 19
     },
     {
-      "type": "RIGHT_BRACE",
-      "lexeme": "}",
+      "type": "IDENTIFIER",
+      "lexeme": "T",
       "line": 9,
-      "column": 1
+      "column": 20
+    },
+    {
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
+      "line": 9,
+      "column": 21
     },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 9,
-      "column": 2
+      "column": 22
     },
     {
       "type": "NEWLINE",
@@ -276,869 +420,2239 @@
       "line": 10,
       "column": 1
     },
+    {
+      "type": "COMMENT",
+      "lexeme": "// Complex custom type, containing two values accessible through properties",
+      "line": 11,
+      "column": 1
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 11,
+      "column": 76
+    },
     {
       "type": "TYPE",
       "lexeme": "type",
-      "line": 11,
+      "line": 12,
       "column": 1
     },
     {
       "type": "WHITESPACE",
       "lexeme": " ",
-      "line": 11,
+      "line": 12,
       "column": 5
     },
     {
       "type": "IDENTIFIER",
-      "lexeme": "LatitudeDiff",
-      "line": 11,
+      "lexeme": "GeoLocation",
+      "line": 12,
       "column": 6
     },
     {
-      "type": "LESS",
-      "lexeme": "<",
-      "line": 11,
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 12,
+      "column": 17
+    },
+    {
+      "type": "LEFT_BRACE",
+      "lexeme": "{",
+      "line": 12,
       "column": 18
     },
     {
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       "column": 19
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       "column": 1
     },
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     {
       "type": "WHITESPACE",
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-    {
-      "type": "NEWLINE",
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     },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 13,
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+      "column": 5
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       "column": 1
     },
     {
       "type": "COMMENT",
-      "lexeme": "// Simple operation defined on our custom types",
-      "line": 14,
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       "column": 1
     },
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-      "type": "NEWLINE",
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-      "line": 16,
-      "column": 47
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     {
       "type": "NEWLINE",
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+      "lexeme": " ",
+      "line": 18,
+      "column": 7
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+      "column": 8
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+      "type": "WHITESPACE",
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+      "column": 19
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+      "column": 20
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       "column": 1
     },
     {
       "type": "COMMENT",
-      "lexeme": "// Simple custom type with a constraint",
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-    {
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-      "line": 19,
-      "column": 1
-    },
-    {
-      "type": "WHITESPACE",
-      "lexeme": " ",
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       "line": 19,
       "column": 5
     },
-    {
-      "type": "IDENTIFIER",
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-    {
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-      "line": 19,
-      "column": 36
-    },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 19,
-      "column": 37
+      "column": 79
     },
     {
-      "type": "NEWLINE",
-      "lexeme": "\n",
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       "line": 20,
       "column": 1
     },
     {
       "type": "COMMENT",
-      "lexeme": "// Predefined custom constraints that can be referenced in other definitions",
+      "lexeme": "// i.e. you can subtract a GeoLocation from another GeoLocation, resulting",
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+      "column": 5
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 20,
+      "column": 79
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       "line": 21,
       "column": 1
     },
+    {
+      "type": "COMMENT",
+      "lexeme": "// in a Difference of GeoLocations",
+      "line": 21,
+      "column": 5
+    },
     {
       "type": "NEWLINE",
       "lexeme": "\n",
       "line": 21,
-      "column": 77
+      "column": 39
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     {
-      "type": "CONSTRAINT",
-      "lexeme": "constraint",
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+      "lexeme": "    ",
       "line": 22,
       "column": 1
     },
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+      "type": "OP",
+      "lexeme": "op",
+      "line": 22,
+      "column": 5
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+    {
+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 22,
+      "column": 7
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+      "column": 8
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+      "type": "LEFT_PAREN",
+      "lexeme": "(",
+      "line": 22,
+      "column": 15
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "GeoLocation",
+      "line": 22,
+      "column": 16
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+    {
+      "type": "RIGHT_PAREN",
+      "lexeme": ")",
+      "line": 22,
+      "column": 27
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+      "type": "WHITESPACE",
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+      "line": 22,
+      "column": 28
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+      "lexeme": "->",
+      "line": 22,
+      "column": 29
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+      "type": "WHITESPACE",
+      "lexeme": " ",
+      "line": 22,
+      "column": 31
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+    {
+      "type": "IDENTIFIER",
+      "lexeme": "Difference",
+      "line": 22,
+      "column": 32
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+      "type": "LEFT_BRACKET",
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+      "line": 22,
+      "column": 42
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "GeoLocation",
+      "line": 22,
+      "column": 43
+    },
+    {
+      "type": "RIGHT_BRACKET",
+      "lexeme": "]",
+      "line": 22,
+      "column": 54
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+      "lexeme": "\n",
+      "line": 22,
+      "column": 55
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+      "line": 23,
+      "column": 1
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+    {
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+      "line": 23,
+      "column": 2
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+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 24,
+      "column": 1
+    },
+    {
+      "type": "COMMENT",
+      "lexeme": "// For complex generics, you need to specify how the genericity the properties",
+      "line": 25,
+      "column": 1
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 25,
+      "column": 79
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+    {
+      "type": "COMMENT",
+      "lexeme": "// are handled",
+      "line": 26,
+      "column": 1
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 26,
+      "column": 15
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+      "line": 27,
+      "column": 1
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     {
       "type": "WHITESPACE",
       "lexeme": " ",
-      "line": 22,
-      "column": 11
+      "line": 27,
+      "column": 5
     },
     {
       "type": "IDENTIFIER",
-      "lexeme": "Positive",
-      "line": 22,
-      "column": 12
+      "lexeme": "Difference",
+      "line": 27,
+      "column": 6
+    },
+    {
+      "type": "LEFT_BRACKET",
+      "lexeme": "[",
+      "line": 27,
+      "column": 16
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+    {
+      "type": "IDENTIFIER",
+      "lexeme": "GeoLocation",
+      "line": 27,
+      "column": 17
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+    {
+      "type": "RIGHT_BRACKET",
+      "lexeme": "]",
+      "line": 27,
+      "column": 28
     },
     {
       "type": "WHITESPACE",
       "lexeme": " ",
-      "line": 22,
+      "line": 27,
+      "column": 29
+    },
+    {
+      "type": "LEFT_BRACE",
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+      "line": 27,
+      "column": 30
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 27,
+      "column": 31
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+    {
+      "type": "WHITESPACE",
+      "lexeme": "    ",
+      "line": 28,
+      "column": 1
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+    {
+      "type": "IDENTIFIER",
+      "lexeme": "lat",
+      "line": 28,
+      "column": 5
+    },
+    {
+      "type": "COLON",
+      "lexeme": ":",
+      "line": 28,
+      "column": 8
+    },
+    {
+      "type": "WHITESPACE",
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+      "line": 28,
+      "column": 9
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "Difference",
+      "line": 28,
+      "column": 10
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+    {
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+      "line": 28,
       "column": 20
     },
     {
-      "type": "EQUAL",
-      "lexeme": "=",
-      "line": 22,
+      "type": "IDENTIFIER",
+      "lexeme": "Latitude",
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       "column": 21
     },
     {
-      "type": "WHITESPACE",
-      "lexeme": " ",
-      "line": 22,
-      "column": 22
+      "type": "RIGHT_BRACKET",
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+      "line": 28,
+      "column": 29
     },
     {
-      "type": "UNDERSCORE",
-      "lexeme": "_",
-      "line": 22,
-      "column": 23
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 28,
+      "column": 30
+    },
+    {
+      "type": "WHITESPACE",
+      "lexeme": "    ",
+      "line": 29,
+      "column": 1
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+    {
+      "type": "IDENTIFIER",
+      "lexeme": "lon",
+      "line": 29,
+      "column": 5
+    },
+    {
+      "type": "COLON",
+      "lexeme": ":",
+      "line": 29,
+      "column": 8
     },
     {
       "type": "WHITESPACE",
       "lexeme": " ",
-      "line": 22,
+      "line": 29,
+      "column": 9
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "Difference",
+      "line": 29,
+      "column": 10
+    },
+    {
+      "type": "LEFT_BRACKET",
+      "lexeme": "[",
+      "line": 29,
+      "column": 20
+    },
+    {
+      "type": "IDENTIFIER",
+      "lexeme": "Longitude",
+      "line": 29,
+      "column": 21
+    },
+    {
+      "type": "RIGHT_BRACKET",
+      "lexeme": "]",
+      "line": 29,
+      "column": 30
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 29,
+      "column": 31
+    },
+    {
+      "type": "RIGHT_BRACE",
+      "lexeme": "}",
+      "line": 30,
+      "column": 1
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 30,
+      "column": 2
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 31,
+      "column": 1
+    },
+    {
+      "type": "COMMENT",
+      "lexeme": "// Simple operation defined on our custom types",
+      "line": 32,
+      "column": 1
+    },
+    {
+      "type": "NEWLINE",
+      "lexeme": "\n",
+      "line": 32,
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     {
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