Index: main.d
==================================================================
--- main.d
+++ main.d
@@ -4,14 +4,14 @@
  *
  * Entry point for Polemy interpreter.
  */
 
 import std.stdio;
-import polemy.lex;
-import polemy.parse;
-
-static ~this() { readln(); } // workaround for enabling "pause" under Poseidon
+import polemy.eval;
+
+version(unittest)
+	static ~this() { readln(); } // workaround for enabling "pause" under Poseidon
 
 void main()
 {
 	writeln( "test ok" );
 }

Index: polemy/ast.d
==================================================================
--- polemy/ast.d
+++ polemy/ast.d
@@ -1,6 +1,6 @@
-/*
+/**
  * Authors: k.inaba
  * License: NYSL 0.9982 http://www.kmonos.net/nysl/
  *
  * Syntax tree for Polemy programming language.
  */

Index: polemy/eval.d
==================================================================
--- polemy/eval.d
+++ polemy/eval.d
@@ -9,10 +9,11 @@
 import polemy.lex : LexPosition;
 import polemy.ast;
 import polemy.parse;
 import polemy.runtime;
 import std.typecons;
+import std.stdio;
 
 Context createGlobalContext()
 {
 	auto ctx = new Context;
 	ctx.add("+", new FunValue(delegate Value(immutable LexPosition pos, Value[] args){
@@ -44,10 +45,16 @@
 			throw new PolemyRuntimeException("/ takes two arguments!! ["~to!string(pos)~"]");
 		if( auto x = cast(IntValue)args[0] )
 			if( auto y = cast(IntValue)args[1] )
 				return new IntValue(x.data/y.data);
 		throw new PolemyRuntimeException("cannot add non-integers ["~to!string(pos)~"]");
+	}));
+	ctx.add("print", new FunValue(delegate Value(immutable LexPosition pos, Value[] args){
+		foreach(a; args)
+			write(a);
+		writeln("");
+		return new UndefinedValue;
 	}));
 	return ctx;
 }
 
 Tuple!(Value,"val",Context,"ctx") evalString(T...)(T params)
@@ -169,5 +176,10 @@
 {
 	auto r = evalString(`var x = 1; var f = fun(){x=x+1;}; f(); f(); f();`);
 	assert( r.ctx["x"] == new IntValue(BigInt(4)) );
 	assert( r.val == new IntValue(BigInt(4)) );
 }
+unittest
+{
+	evalString(`print("Hello, world!");`);
+	evalString(`print(fun(){});`);
+}

Index: polemy/lex.d
==================================================================
--- polemy/lex.d
+++ polemy/lex.d
@@ -45,12 +45,17 @@
 }
 
 /// Represents a lexer token
 
 class Token
-{
-	enum Kind {identifier, stringLiteral, number};
+{
+	/// currently we have three kinds of token
+	enum Kind {
+		identifier, /// anything other than others
+		stringLiteral, /// "string literal"
+		number /// 42
+	};
 	immutable LexPosition pos;  /// position where the token occurred in the source
 	immutable string      str;  /// the token string itself
 	immutable Kind        kind; /// which kind of token?
 
 	mixin SimpleConstructor;

Index: polemy/parse.d
==================================================================
--- polemy/parse.d
+++ polemy/parse.d
@@ -1,6 +1,6 @@
-/*
+/**
  * Authors: k.inaba
  * License: NYSL 0.9982 http://www.kmonos.net/nysl/
  *
  * Parser for Polemy programming language
  */

Index: polemy/runtime.d
==================================================================
--- polemy/runtime.d
+++ polemy/runtime.d
@@ -20,31 +20,38 @@
 
 class UndefinedValue : Value
 {
 	mixin SimpleConstructor;
 	mixin SimpleCompare;
+	override string toString() const { return "(undefined)"; }
 }
 
 class IntValue : Value
 {
 	BigInt data;
 	mixin SimpleConstructor;
 	mixin SimpleCompare;
+	override string toString() const {
+		const(char)[] cs; data.toString((const(char)[] s){cs=s;}, null);
+		return to!string(cs);
+	}
 }
 
 class StrValue : Value
 {
 	string data;
 	mixin SimpleConstructor;
 	mixin SimpleCompare;
+	override string toString() const { return data; }
 }
 
 class FunValue : Value
 {
 	Value delegate(immutable LexPosition pos, Value[]) data;
 	mixin SimpleConstructor;
 	Value call(immutable LexPosition pos, Value[] args) { return data(pos,args); }
+	override string toString() const { return sprintf!"(function:%s:%s)"(data.ptr,data.funcptr); }
 }
 import std.stdio;
 class Context
 {
 	Context       parent;

Index: polemy/tricks.d
==================================================================
--- polemy/tricks.d
+++ polemy/tricks.d
@@ -41,11 +41,11 @@
 			static if(this.tupleof.length>0)
 				this.tupleof = params;
 		}
 }
 
-/// Mixing-in the (MOST-DERIVED) member-wise comparator for a class
+/// Mixing-in the MOST-DERIVED-member-wise comparator for a class
 
 /*mixin*/ template SimpleCompare()
 {
 	override bool opEquals(Object rhs_) const
 	{