query {rolog}

Create a query

Description

Create a query

Usage

query(
  query = call("member", expression(X), list(quote(a), "b", 3L, 4, TRUE, expression(Y))),
  options = NULL,
  env = globalenv()
)

Arguments

query

an R call. The R call consists of symbols, integers and real numbers, character strings, boolean values, expressions, lists, and other calls. Vectors of booleans, integers, floating point numbers, and strings with length N > 1 are translated to prolog compounds !/N, %/N, #/N and $$/N, respectively. The names can be modified with the options below.

options

This is a list of options controlling translation from and to prolog.

• boolvec (see option rolog.boolvec, default is !) is the name of the prolog compound for vectors of booleans.

• intvec, realvec, charvec define the compound names for vectors of integers, doubles and strings, respectively (defaults are %, # and $$).

• If scalar is TRUE (default), vectors of length 1 are translated to scalar prolog elements. If scalar is FALSE, vectors of length 1 are also translated to compounds.

env

The R environment in which the query is run (default: globalenv()). This is mostly relevant for r_eval/2.

Details

SWI-Prolog does not allow multiple open queries. If another query is open, it it is closed and a warning is shown.

Value

If the creation of the query succeeds, TRUE.

See Also

once() for a query that is submitted only a single time.

findall() for a query that is submitted until it fails.

Examples

query(call("member", expression(X), list(quote(a), "b", 3L, 4, TRUE, expression(Y))))
submit() # X = a
submit() # X = "b"
clear()

query(call("member", expression(X), list(quote(a), "b", 3L, 4, TRUE, expression(Y),
  NA, NaN, Inf, NULL, function(x) {y <- sin(x); y^2})))
submit() # X = a
submit() # X = "b"
submit() # X = 3L
submit() # X = 4.0
submit() # X = TRUE
submit() # X = expression(Y) or Y = expression(X)
submit() # X = NA
submit() # X = NaN
submit() # X = Inf
submit() # X = NULL
submit() # X = function(x) {y <- sin(x); y^2}))
submit() # FALSE (no more results)
submit() # warning that no query is open

query(call("member", expression(X), list(quote(a), "b", 3L, 4)))
query(call("member", expression(X), list(TRUE, expression(Y)))) # warning that another query is open
clear()