diff --git a/sjscript/src/sjscript/Expression.d b/sjscript/src/sjscript/Expression.d
new file mode 100644
index 0000000..895a523
--- /dev/null
+++ b/sjscript/src/sjscript/Expression.d
@@ -0,0 +1,51 @@
+/// License: MIT
+module sjscript.Expression;
+
+import std.variant;
+
+///
+struct Expression {
+ public:
+  ///
+  Term opBinary(string op : "+", T)(T rhs) const {
+    return Expression(terms ~ rhs);
+  }
+  ///
+  Term opBinary(string op : "-", T)(T rhs) const {
+    return Expression(terms ~ rhs*(-1f));
+  }
+
+  ///
+  Term[] terms;
+}
+
+///
+struct Term {
+ public:
+  ///
+  alias Value = Algebraic!(float, string, FunctionCall);
+
+  ///
+  Term opBinary(string op : "*", T)(T rhs) const {
+    return Term(multipled_values ~ Value(rhs), divided_values);
+  }
+  ///
+  Term opBinary(string op : "/", T)(T rhs) const {
+    return Term(multipled_values, divided_values ~ Value(rhs));
+  }
+
+  ///
+  Value[] multipled_values;
+  ///
+  Value[] divided_values;
+}
+
+///
+struct FunctionCall {
+ public:
+  ///
+  string name;
+
+  ///
+  Expression[] args;
+}
diff --git a/sjscript/src/sjscript/ParametersBlock.d b/sjscript/src/sjscript/ParametersBlock.d
new file mode 100644
index 0000000..bb91003
--- /dev/null
+++ b/sjscript/src/sjscript/ParametersBlock.d
@@ -0,0 +1,53 @@
+/// License: MIT
+module sjscript.ParametersBlock;
+
+import sjscript.Expression,
+       sjscript.Token;
+
+///
+struct ParametersBlock {
+ public:
+  ///
+  string name;
+
+  ///
+  Period period;
+
+  ///
+  Parameter[] parameters;
+
+  ///
+  TokenPos pos;
+}
+
+///
+struct Period {
+ public:
+  ///
+  size_t start;
+
+  ///
+  size_t end;
+}
+
+///
+enum ParameterType {
+  Assign,
+  AddAssign,
+}
+
+///
+struct Parameter {
+ public:
+  ///
+  string name;
+
+  ///
+  ParameterType type;
+
+  ///
+  Expression rhs;
+
+  ///
+  TokenPos pos;
+}
diff --git a/sjscript/src/sjscript/Token.d b/sjscript/src/sjscript/Token.d
index c02604f..0bdb0d4 100644
--- a/sjscript/src/sjscript/Token.d
+++ b/sjscript/src/sjscript/Token.d
@@ -7,6 +7,9 @@ import std.algorithm,
 
 import dast.tokenize;
 
+///
+alias TokenPos = dast.tokenize.TokenPos;
+
 ///
 enum TokenType {
   @TextFuncMatcher!((string text, string next) {