# Reserved Names for Functions and Variables

Variable or function names must start with a non-number, and must not contain any of the following symbols:

.   ,   *   /   +   -   ^   =   <   >   #   (   )   [   ]  { }  @   ;   ’   ” ! % ~ :

Variable or function names are not case-sensitive. User-defined names can be any length, but they may be truncated when printed and in plot captions, due to line-length limitations. In general, names may be chosen arbitrarily, although they must not be the same as a FISH statement or a predefined variable or function. For instance, a FISH variable named comp is not acceptable because this is the built-in function to get or set a vector or tensor component.

User-defined variables may represent Booleans, single numbers, strings, lists, matrices, maps, tensors, structures, vectors, pointers, or arrays. The list of data types is given in Data Types. The methods available for use with these types are listed in the FISH Function Index.