local functions block

[alashworth]

Issue by bgoodri Tuesday Aug 23, 2016 at 03:19 GMT Originally opened as https://github.com/stan-dev/stan/issues/2024

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Summary:

The Stan language should have the ability to create user-defined member functions of the model class

Description:

At the last meeting, we proposed adding a new block to the Stan language that perhaps could be called local functions that would go after transformed data. The Stan syntax would be the same as in the functions block but unlike the user-defined functions in the functions block the user-defined functions in the local functions block could refer to objects in the data and transformed data blocks without explicitly passing them as arguments. This would make such functions much easier to use than integrate_ode, which requires fixed arguments to be passed in a very clunky way. It might look like

data {
  int<lower=1> N;
}
transformed data {
  int<lower=2> two_N;
  two_N = 2 * N;
}
local functions {
  void what_is_2N() {
    print("2N = ", two_N);
  }
}

Reproducible Steps:

Does not currently exist.

Current Output:

Does not currently exist.

Expected Output:

Whatever the user-defined function returns

Additional Information:

None

Current Version:

v2.11.0

[alashworth]

Comment by bob-carpenter Tuesday Aug 23, 2016 at 12:37 GMT

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I take it this requires all four flavors of function:

• _lp : has access to density so target += and ~ statements may be used (only callable in model block)
• _rng: has access to PRNG, so _rng functions may be used (only callable in generated quantities block)
• _lpdf, _lpmf, _lcdf, _lccdf : pdf and pmf may be used on right-hand side of sampling statements, called with vertical bar notation (can be used anywhere, but sampling sttements restricted to model block)
• none-of-the-above: can't do any of the above, but may be used anywhere

[alashworth]

Comment by bgoodri Tuesday Aug 23, 2016 at 13:05 GMT

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I would think that the possible types would be the same as for global functions the user defines.

On Aug 23, 2016 8:37 AM, "Bob Carpenter" notifications@github.com wrote:

I take it this requires all four flavors of function:

-

_lp : has access to density so target += and ~ statements may be used

_rng: has access to PRNG, so _rng functions may be used

_lpdf, _lpmf : may be used on right-hand side of sampling statements

none-of-the-above: can't do any of the above, but may be used anywhere

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