Every
variable used in a Stan program must have a declared data type. Only
values of that type will be assignable to the variable (except for
temporary states of transformed data and transformed parameter
values). This follows the convention of programming languages like
C++, not the conventions of scripting languages like Python or
statistical languages such as R or BUGS.</p>
<p>The motivation for strong, static typing is threefold.</p>
<ol style="list-style-type: decimal">
<li>Strong typing forces the pro