Consider this code:

fun = Compile[{}, 
    rn = RandomChoice[{0.8, 0.1, 0.1} -> {1, 2, 3}];
    If[rn > 1, Throw[j]]
    , {j, 1, 10}]]
  , CompilationTarget -> "C"]

At each iteration a number randomly is chosen and if it is greater than 1, then the code must return the number of the iteration in which the condition is satisfied.

If I don't compile to C, then everything is fine, but if I compile to C then I get this error message:

CompiledFunction::cflist: Nontensor object generated; proceeding with uncompiled evaluation. >>

In the documents says it happen when someone tries to add two unequal-in-length lists. I can't see how this cause the problem as I don't add any two lists in the code.

Using Return intead of Throw makes a similar error.


I think this question might be relevant to this one. I think because sometimes the Throw returns Null there is error.

  • $\begingroup$ Is it possible to define the output so that it can returns Null too? $\endgroup$
    – MOON
    Feb 11, 2015 at 14:16
  • $\begingroup$ Suppose I give the result of the If statement to another variable like x. Is it possible to check whether x is Null and if so set it equal to 0? Like If[x==Null,x=0] $\endgroup$
    – MOON
    Feb 11, 2015 at 14:29

1 Answer 1


If you localize rn, then it works.

fun = Compile[{}, 
   Catch[Do[rn = RandomChoice[{0.8, 0.1, 0.1} -> {1, 2, 3}];
     If[rn > 1, Throw[j]], {j, 1, 10}]]], CompilationTarget -> "C"]

Table[fun[], {10}]
(*  {1, 1, 2, 3, 3, 10, 2, 11, 2, 7}  *)
  • $\begingroup$ why does this ever return 11? $\endgroup$
    – george2079
    Feb 11, 2015 at 21:57
  • $\begingroup$ @george2079 In the WVM code, j is 11 when the loop ends and the instruction right after the loop assigns the value j to the return register. See yashar's other post, mathematica.stackexchange.com/questions/73786/…, for a discussion. (I don't think it ought to return 11, of course. It's arguably a bug in the compiler.) $\endgroup$
    – Michael E2
    Feb 11, 2015 at 22:35
  • $\begingroup$ Is there a way to see the generated c code? in any case putting ';0' , or whatever value you want, after the Do inside Catch should let you control the default return value.. $\endgroup$
    – george2079
    Feb 11, 2015 at 23:37
  • $\begingroup$ @george2079 I made such a comment to the OP's q., which I since deleted because it contained an incorrect suggestion of what was going wrong. yashar didn't seem interested. The C code is stored in a directory. Compile with Compiler`$CCompilerOptions = {"CleanIntermediate" -> False} and inspect fun // InputForm; the directory will be in a subdirectory of the directory containing the .dylib file (at least on Mac OSX, Mma V10.0.2). $\endgroup$
    – Michael E2
    Feb 12, 2015 at 0:24

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