Improve and correct IO UI and add tests

tests/arrow.node

@@ -0,0 +1,4 @@
+node main (i: int) returns (o: int);
+let
+    o = 1 -> 2 -> 3;
+tel

tests/counting.node

@@ -0,0 +1,16 @@
+-- count the number of top between two tick
+node counting (tick:bool; top:bool)
+returns (o: int);
+var v, o1: int;
+let o = if tick then v else 0 -> (pre o) + v;
+	v = if top then 1 else 0
+tel;
+
+node main (i: int)
+returns (o: int);
+let
+    -- 0 means no `tick` and no `top`
+    -- 1 means `tick`
+    -- 2 means `top`
+    o = counting(i = 1, i = 2)
+tel;

tests/pre.node

@@ -1,4 +1,4 @@
-node n2 (i: int) returns (o: bool);
+node main (i: int) returns (o: bool);
 let
     o = pre (true and pre( i = pre(pre(i))));
 tel

tests/reset.node

@@ -0,0 +1,15 @@
+-- counter of `top`s until `reset` condition holds
+node counting (tick: bool) returns (o: int);
+var v: int;
+let
+  o = v -> (pre o) + v;
+  v = if tick then 1 else 0
+tel
+
+node main (i: int) returns (o: int);
+let
+  -- 0 means no `top` and no `reset`
+  -- 1 means `top`
+  -- 2 means `reset`
+  o = reset counting(i = 1) every (i = 2);
+tel

tests/when_merge.node

@@ -0,0 +1,14 @@
+node test (i: int) returns (o: int);
+var x, y: int;
+let
+    x = (1 / i) when (i <> 0);
+    y = 0 when (not (i <> 0));
+    o = merge (i <> 0) x y;
+tel
+
+node main (i: int) returns (o: int);
+var garbage: int;
+let
+    garbage = test(0);
+    o = test(1);
+tel