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evaluation - Get the current iteration count


I would like to be able to get the current iteration count, the one that if exceeds $IterationLimit makes the evaluation stop.


After not finding a magical variable that stores this value, or a magical built-in that retrieves it, I thought about TraceScan.



According to the documentation of $IterationLimit,



$IterationLimit gives an upper limit on the length of any list that can be generated by Trace

However, a quick test shows that this is not so simple. Let's define


ClearAll[f]
f[i_] := f[i - 1]
f[0] := "Yeah"

Now,



Block[{$IterationLimit = 20},
 Trace[f[18]] // Length//Print;
 Trace[f[18], TraceDepth -> 1] // Length//Print;
 f[18]
 ]

prints 56 and 38 respectively, while f[18]'s evaluation finishes successfully.


Looking at the output of the last trace, we see that the before and after argument evaluation are being traced. So,


Trace[f[3], TraceDepth -> 1]   
(* {f[3],f[3-1],f[2],f[2-1],f[1],f[1-1],f[0],Yeah} *)


Notice that the "two outputs per iteration" rule doesn't hold if we add a definition like f[3]=f[1], in which case


Trace[f[5], TraceDepth -> 1]
(* {f[5],f[5-1],f[4],f[4-1],f[3],f[1],f[1-1],f[0],Yeah} *)

If this happened, a hacky workround could exist along the lines of


SetAttributes[trackIterations, HoldFirst];
trackIterations[code_] := Block[{iterationCounter = 0},
  TraceScan[iterationCounter += 1/2, code, TraceDepth -> 1]
  ]


Question


How can I get that counter, or alternatively, how can I make Trace only trace once each iteration?




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