Straightforward While lexer, parser and interpreter

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diff --git a/paper/While/Simple.icl b/paper/While/Simple.icl
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+implementation module Simple
+
+import StdString
+
+import WhileCommon
+import Common
+
+instance toString Stm
+where
+	toString (Ass v a) = v <+ " := " <+ a
+	toString (If b s1 s2) = "if " <+ b <+ " then " <+ s1 <+ " else " <+ s2
+	toString (While b s) = "while " <+ b <+ " do " <+ s
+	toString Skip = "skip"
+	toString (Compose s1 s2) = s1 <+ "; " <+ s2
+
+instance run Stm
+where
+	run (Ass v e) st = eval e st >>= \r -> pure (\w -> if (w==v) (pure r) (st w))
+	run (If b s1 s2) st = eval b st >>= \r -> run (if r s1 s2) st
+	run w=:(While b s) st = eval b st >>= \r -> if r (run s st >>= \st` -> run w st`) (pure st)
+	run Skip st = pure st
+	run (Compose s1 s2) st = run s1 st >>= \st` -> run s2 st`