wonky error messages in calculate

[goldingn]

The error messages are wonky for calculate(), in the event a user provides a greta array with unknown values:

library(greta)
#> 
#> Attaching package: 'greta'
#> The following objects are masked from 'package:stats':
#> 
#>     binomial, cov2cor, poisson
#> The following objects are masked from 'package:base':
#> 
#>     %*%, apply, backsolve, beta, chol2inv, colMeans, colSums, diag,
#>     eigen, forwardsolve, gamma, identity, rowMeans, rowSums, sweep,
#>     tapply

# Error message mentions lapply?
# It says we need to provide values for a, but not that we could also set `nsim`
a <- normal(0, 1)
#> ℹ Initialising python and checking dependencies, this may take a moment.
#> ✔ Initialising python and checking dependencies ... done!
#> 
calculate(a)
#> Error in `lapply()` at greta/R/calculate.R:407:5:
#> ! Please provide values for the following 1 <greta_array>:
#> `a`
#> Backtrace:
#>      ▆
#>   1. └─greta::calculate(a)
#>   2.   ├─base::with(...) at greta/R/calculate.R:162:3
#>   3.   ├─reticulate:::with.python.builtin.object(...)
#>   4.   │ ├─base::tryCatch(...)
#>   5.   │ │ └─base (local) tryCatchList(expr, classes, parentenv, handlers)
#>   6.   │ └─base::force(expr)
#>   7.   └─greta:::calculate_list(...) at greta/R/calculate.R:247:7
#>   8.     └─base::lapply(...) at greta/R/calculate.R:407:5
#>   9.       └─greta (local) FUN(X[[i]], ...)
#>  10.         └─rlang::abort(message = msg, call = call) at greta/R/checkers.R:732:5

# Error message mentions lapply?
# It says it can't find the name of an object, but not why it is looking for one.
# It also doesn't say that we could also set `nsim`
b <- 1 + normal(0, 1)
calculate(b)
#> Error in `lapply()` at greta/R/calculate.R:407:5:
#> ! The names of the missing <greta_array>s could not be detected
#> Backtrace:
#>      ▆
#>   1. └─greta::calculate(b)
#>   2.   ├─base::with(...) at greta/R/calculate.R:162:3
#>   3.   ├─reticulate:::with.python.builtin.object(...)
#>   4.   │ ├─base::tryCatch(...)
#>   5.   │ │ └─base (local) tryCatchList(expr, classes, parentenv, handlers)
#>   6.   │ └─base::force(expr)
#>   7.   └─greta:::calculate_list(...) at greta/R/calculate.R:247:7
#>   8.     └─base::lapply(...) at greta/R/calculate.R:407:5
#>   9.       └─greta (local) FUN(X[[i]], ...)
#>  10.         └─rlang::abort(message = msg, call = call) at greta/R/checkers.R:732:5

^{Created on 2025-03-27 with reprex v2.0.2}

[njtierney]

Thanks for this!

The error is happening in https://github.com/greta-dev/greta/blob/master/R/checkers.R#L701

I need to dig a bit deeper as to why this is happening - it appears that the wrong error message is being triggered. In this instance we would expect it to say it is missing the nsim