multiple variable declarations on one line

[tpapp]

Would it be possible to allow multiple declarations on one line, that avoid repeating the var_decl part of the grammar? Eg

real alpha, beta, gamma[5];
real<lower=0> a, b[3, 4];

that would be equivalent to

real alpha;
real beta;
real gamma[5];
real<lower=0> a;
real<lower=0> b[3, 4];

and similarly for other types.

This would allow more compact code, could factor out common parts. As far as I understand, this would only change the surface syntax (parser) a bit, and would require no change to the internals.

[bob-carpenter]

Thanks for creating the issue.

It's been on our to-do list from the get go, but never got transferred
to an issue.

There are two related features, both of which also need issues:

1. Allowing compound declaration and assignment where relevant (transformed
   data, transformed parameters, generated quantities, local variables, e.g.,

real alpha <- 1;

1. Allowing inline local variable declarations, like in C++, e.g.,

beta <- 2;
real alpha;  // local variable declaration
alpha <- 3;  

• Bob

On Nov 20, 2014, at 11:47 AM, tpapp notifications@github.com wrote:

Would it be possible to allow multiple declarations on one line, that avoid repeating the var_decl part of the grammar? Eg

real alpha, beta, gamma[5];
real<lower=0> a, b[3, 4];

that would be equivalent to

real alpha;
real beta;
real gamma[5];
real<lower=0> a;
real<lower=0> b[3, 4];

and similarly for other types.

This would allow more compact code, could factor out common parts. As far as I understand, this would only change the surface syntax (parser) a bit, and would require no change to the internals.

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Reply to this email directly or view it on GitHub.

[bob-carpenter]

@andrewgelman has been asking for this feature since Stan 1.0. I've even used it to compress slides.

I'm less keen on the idiom myself and we don't use it much in our own C++, but I'm OK with someone adding it to the language.

[rok-cesnovar]

This was addressed in #670 and can be closed.

data {
  real x, y, z;
  array[5] int i, j;
}
transformed data {
  real a = 5, b = 6;
  real c = 5, d, e = 7;
}

You can not do real alpha, beta, gamma[5]; as gamma is of a different type.

You can do

array[5] real alpha, beta, gamma;