Diagnostic Functions

t_value
_print(t_value v, t_int deps = 0, t_bool verbose = FALSE)

Print the value v to standard output followed by a newline, and return v. What gets printed depends on v's type. If v is of type t_err, ERR is printed. If v is of type t_bool, TRUE or FALSE is printed. If v is of type t_int, its decimal value is printed.

The printed representation of a t_text value is <file 0xXXXXXXXX> if verbose is false and the text is represented by a backing file, in which case XXXXXXXX is the file's hexadecimal identifier. Otherwise, it is the text value's contents enclosed in double quotes.

The printed representation of a t_list value containing the values $v_1, v_2, \ldots, v_k$ is <  $p_1, p_2, \ldots, p_k$ >, where $p_i$ denotes the printed representation of the value $v_i$.

The printed representation of a t_binding value containing the (name, value) pairs $(n_1, v_1), (n_2, v_2), \ldots, (n_k, v_k)$ is [  $n_1 = p_1, \ldots, n_k = p_k$ ], where again $p_i$ denotes the printed representation of the value $v_i$.

The printed representation of a t_closure value is <Model name> if the closure is represented by a model, in which case name is a name for the model file in the repository. Otherwise, if verbose is true, it is the complete list of formals, body, and context; if not it is simply <Closure>.

If deps is greater than zero, the value's dependencies are also printed. In the current implementation, values of 1 and 2 provide different levels of detail. This feature is meant for debugging the evaluator itself.

Typically, _print is used for debugging purposes, and its result is ignored. However, it is important to remember that _print is a function, not a statement. Hence, one cannot simply write:

  _print(v);

inside a function body. Instead, the call to _print must be used in a functional way, such as:

  dummy = _print(v);

Note also that efficient implementations of the Vesta language will cache function results and re-use those cached results whenever it is safe to do so. Calls to the _print function itself are never cached. However, the _print function's side effect of printing to the terminal is not repeated whenever the call to _print is skipped due to a higher level hit on the function cache.

t_bool
_assert(t_bool cond, t_value msg)

If the value cond is true, return true. Otherwise, print the value msg as with the _print primitive, then terminate the evaluation with a runtime error. As a diagnostic aid, our implementation allows the context of a false assertion and/or a stack trace to be printed as well, if selected by command-line options to the evaluator. Note that, like _print, _assert is a function, not a statement.