Clingo C API
C API for clingo providing high level functions to control grounding and solving.
ast.c

The example shows how to rewrite a non-ground logic program.

Output

./ast 0
Solving with enable = false...
Model:
Solving with enable = true...
Model: enable a
Model: enable b
Solving with enable = false...
Model:

Code

#include <clingo.h>
#include <stdlib.h>
#include <stdio.h>
bool print_model(clingo_model_t const *model) {
bool ret = true;
clingo_symbol_t *atoms = NULL;
size_t atoms_n;
clingo_symbol_t const *it, *ie;
char *str = NULL;
size_t str_n = 0;
// determine the number of (shown) symbols in the model
if (!clingo_model_symbols_size(model, clingo_show_type_shown, &atoms_n)) { goto error; }
// allocate required memory to hold all the symbols
if (!(atoms = (clingo_symbol_t*)malloc(sizeof(*atoms) * atoms_n))) {
clingo_set_error(clingo_error_bad_alloc, "could not allocate memory for atoms");
goto error;
}
// retrieve the symbols in the model
if (!clingo_model_symbols(model, clingo_show_type_shown, atoms, atoms_n)) { goto error; }
printf("Model:");
for (it = atoms, ie = atoms + atoms_n; it != ie; ++it) {
size_t n;
char *str_new;
// determine size of the string representation of the next symbol in the model
if (!clingo_symbol_to_string_size(*it, &n)) { goto error; }
if (str_n < n) {
// allocate required memory to hold the symbol's string
if (!(str_new = (char*)realloc(str, sizeof(*str) * n))) {
clingo_set_error(clingo_error_bad_alloc, "could not allocate memory for symbol's string");
goto error;
}
str = str_new;
str_n = n;
}
// retrieve the symbol's string
if (!clingo_symbol_to_string(*it, str, n)) { goto error; }
printf(" %s", str);
}
printf("\n");
goto out;
error:
ret = false;
out:
if (atoms) { free(atoms); }
if (str) { free(str); }
return ret;
}
typedef struct {
clingo_ast_t *atom;
} on_statement_data;
// adds atom enable to all rule bodies
bool on_statement (clingo_ast_t *stm, on_statement_data *data) {
bool ret = true;
clingo_ast_t *lit = NULL;
size_t size;
if (!clingo_ast_get_type(stm, &type)) { goto error; }
// pass through all statements that are not rules
if (type != clingo_ast_type_rule) {
if (!clingo_program_builder_add(data->builder, stm)) { goto error; }
goto out;
}
// create literal "enable"
if (!clingo_ast_build(clingo_ast_type_literal, &lit, data->loc, clingo_ast_sign_no_sign, data->atom)) {
goto error;
}
if (!clingo_ast_attribute_size_ast_array(stm, clingo_ast_attribute_body, &size)) {
goto error;
}
// append the literal to the rule body
if (!clingo_ast_attribute_insert_ast_at(stm, clingo_ast_attribute_body, size, lit)) {
goto error;
}
// add the rewritten statement to the program
if (!clingo_program_builder_add(data->builder, stm)) { goto error; }
goto out;
error:
ret = false;
out:
if (lit != NULL) {
}
return ret;
}
bool ret = true;
clingo_model_t const *model;
// get a solve handle
if (!clingo_control_solve(ctl, clingo_solve_mode_yield, NULL, 0, NULL, NULL, &handle)) { goto error; }
// loop over all models
while (true) {
if (!clingo_solve_handle_resume(handle)) { goto error; }
if (!clingo_solve_handle_model(handle, &model)) { goto error; }
// print the model
if (model) { print_model(model); }
// stop if there are no more models
else { break; }
}
// close the solve handle
if (!clingo_solve_handle_get(handle, result)) { goto error; }
goto out;
error:
ret = false;
out:
// free the solve handle
return clingo_solve_handle_close(handle) && ret;
}
int main(int argc, char const **argv) {
char const *error_message;
int ret = 0;
clingo_control_t *ctl = NULL;
clingo_symbolic_atoms_t const *atoms = NULL;
clingo_solve_handle_t *handle = NULL;
clingo_ast_t *term = NULL;
on_statement_data data = {NULL, NULL, NULL};
clingo_part_t parts[] = {{ "base", NULL, 0 }};
// create a control object and pass command line arguments
if (!clingo_control_new(argv+1, argc-1, NULL, NULL, 20, &ctl) != 0) { goto error; }
// get the program builder
if (!clingo_control_program_builder(ctl, &data.builder)) { goto error; }
// initialize the location
location.begin_line = location.end_line = 0;
location.begin_column = location.end_column = 0;
location.begin_file = location.end_file = "<rewrite>";
data.loc = &location;
// initilize atom to add
if (!clingo_symbol_create_id("enable", true, &sym)) { goto error; }
if (!clingo_ast_build(clingo_ast_type_symbolic_term, &term, data.loc, sym)) {
goto error;
}
if (!clingo_ast_build(clingo_ast_type_symbolic_atom, &data.atom, term)) {
goto error;
}
// begin building a program
if (!clingo_program_builder_begin(data.builder)) { goto error; }
// get the AST of the program
if (!clingo_ast_parse_string("a :- not b. b :- not a.", (clingo_ast_callback_t)on_statement, &data, NULL, NULL, 20)) { goto error; }
// finish building a program
if (!clingo_program_builder_end(data.builder)) { goto error; }
// add the external statement: #external enable.
if (!clingo_control_add(ctl, "base", NULL, 0, "#external enable.")) {
goto error;
}
// ground the base part
if (!clingo_control_ground(ctl, parts, 1, NULL, NULL)) { goto error; }
// get the program literal coresponding to the external atom
if (!clingo_control_symbolic_atoms(ctl, &atoms)) { goto error; }
if (!clingo_symbolic_atoms_find(atoms, sym, &atm_it)) { goto error; }
if (!clingo_symbolic_atoms_literal(atoms, atm_it, &atm)) { goto error; }
// solve with external enable = false
printf("Solving with enable = false...\n");
if (!solve(ctl, &solve_ret)) { goto error; }
// solve with external enable = true
printf("Solving with enable = true...\n");
if (!solve(ctl, &solve_ret)) { goto error; }
// solve with external enable = false
printf("Solving with enable = false...\n");
if (!solve(ctl, &solve_ret)) { goto error; }
goto out;
error:
if (!(error_message = clingo_error_message())) { error_message = "error"; }
printf("%s\n", error_message);
out:
if (term) { clingo_ast_release(term); }
if (data.atom) { clingo_ast_release(data.atom); }
if (handle) { clingo_solve_handle_close(handle); }
if (ctl) { clingo_control_free(ctl); }
return ret;
}