diff --git a/sjscript/src/sjscript/calculate.d b/sjscript/src/sjscript/calculate.d
index 59db6ec..39c2c2a 100644
--- a/sjscript/src/sjscript/calculate.d
+++ b/sjscript/src/sjscript/calculate.d
@@ -2,13 +2,15 @@
 module sjscript.calculate;
 
 import std.algorithm,
+       std.array,
        std.exception,
        std.format,
        std.math,
        std.traits,
        std.variant;
 
-import sjscript.Expression;
+import sjscript.Expression,
+       sjscript.func;
 
 ///
 enum IsVarStore(T) =
@@ -59,7 +61,6 @@ float CalculateTermValue(VarStore)(in Term.Value value, VarStore vars)
 ///
 float CalculateFunction(VarStore)(in FunctionCall fcall, VarStore vars)
     if (IsVarStore!VarStore) {
-  const args = fcall.args.map!(x => x.CalculateExpression(vars));
-  // TODO: calling function
-  return 0;
+  return fcall.name.CallFunction(
+      fcall.args.map!(x => x.CalculateExpression(vars)).array);
 }
diff --git a/sjscript/src/sjscript/func.d b/sjscript/src/sjscript/func.d
new file mode 100644
index 0000000..3b51752
--- /dev/null
+++ b/sjscript/src/sjscript/func.d
@@ -0,0 +1,43 @@
+/// License: MIT
+module sjscript.func;
+
+import std.algorithm,
+       std.exception,
+       std.math;
+
+///
+float CallFunction(string name, float[] args) {
+  void EnforceArgs(size_t len)() {
+    (args.length == len).enforce("invalid arguments");
+  }
+
+  switch (name) {
+    // ---- misc
+    case "abs":  EnforceArgs!1; return fabs(args[0]);
+    case "sqrt": EnforceArgs!1; return sqrt(args[0]);
+    case "exp":  EnforceArgs!1; return exp(args[0]);
+    case "pow":  EnforceArgs!2; return pow(args[0], args[1]);
+
+    // ---- triangle
+    case "sin": EnforceArgs!1; return sin(args[0]);
+    case "cos": EnforceArgs!1; return cos(args[0]);
+    case "tan": EnforceArgs!1; return tan(args[0]);
+
+    case "asin": EnforceArgs!1; return asin(args[0]);
+    case "acos": EnforceArgs!1; return acos(args[0]);
+    case "atan": EnforceArgs!1; return atan(args[0]);
+
+    case "atan2": EnforceArgs!2; return atan2(args[0], args[1]);
+
+    // ---- rounding
+    case "ceil":  EnforceArgs!1; return ceil(args[0]);
+    case "floor": EnforceArgs!1; return floor(args[0]);
+    case "round": EnforceArgs!1; return round(args[0]);
+
+    // ---- conditional switch
+    case "step":  EnforceArgs!2; return args[1] > args[0]? 1: 0;
+    case "clamp": EnforceArgs!3; return clamp(args[0], args[1], args[3]);
+
+    default: throw new Exception("unknown exception");
+  }
+}
diff --git a/sjscript/test/test01.sj b/sjscript/test/test01.sj
index d60054f..1ec5d7f 100644
--- a/sjscript/test/test01.sj
+++ b/sjscript/test/test01.sj
@@ -1,5 +1,7 @@
 // this is comment
 
+$define pi {3.14}
+
 $define sinwave {
   translate_x = $sinwave_add_x + sin(rtime * $sinwave_hz) * $sinwave_amp_x;
   translate_y = $sinwave_add_y + cos(rtime * $sinwave_hz) * $sinwave_amp_y;
@@ -16,7 +18,7 @@ $define shoot {
   translate_y += __dir_y;
 }
 
-$define beat {0}
+$define beat {sin($pi/4)}
 A [$beat..$beat+10] {
   $define sinwave_add_x {0.5}
   $define sinwave_add_y {0.5}