.TH LIBNORMALFORM_FUNCTION 3 LIBNORMALFORM
.SH NAME
libnormalform_function \- Function with boolean codomain

.SH SYNOPSIS
.nf
#include <libnormalform.h>

struct libnormalform_function {
        int (*\fIevaluate\fP)(void *user_data, void *input);
        void *\fIuser_data\fP;
        const char *\fIidentifier\fP;
        struct libnormalform_function *\fIcopy_for_clone\fP;
        struct libnormalform_function *\fIrelaxation\fP;
        int \fIrequires_relaxation\fP;
};

LIBNORMALFORM_SENTENCE *libnormalform_function(struct libnormalform_function *\fIfunction\fP);
.fi
.PP
Link with
.IR -lnormalform .

.SH DESCRIPTION
The
.BR libnormalform_function ()
function creates a sentence object out
of an application-managed function with
a boolean output.
.PP
.I function->evaluate
is used only be the
.BR libnormalform_evaluate (3)
function to determine the
sentence's value for that specific
call to the
.BR libnormalform_evaluate (3)
function.
.I function->user_data is passed to
.I *function->evaluate
as its first argument, and the function
input is passed as its second argument.
The function is expected to return
.I 1
if the function is true for the input,
.I 0
if the function is false for the input,
and
.I -1
on failure; on failure the function may
optionally set
.IR errno .
.I function->user_data
is only used by the application for
application-defined purposes.
.I function->user_data
may, unlike
.IR function->evalute ,
be
.IR NULL ;
however
.I function->evalute
and
.I function->user_data
need not be set before the
.BR libnormalform_evaluate (3)
function is called.
.PP
See
.BR libnormalform_to_string (3)
for the purpose of
.IR function->identifier ,
it need not be set before the
.BR libnormalform_to_string (3)
function is called.
.PP
See
.BR libnormalform_clone (3)
for the purpose of
.IR function->copy_for_clone ,
it need not be set before the
.BR libnormalform_clone (3)
function is called.
.PP
See
.BR libnormalform_express (3)
for the purpose of
.I function->relaxation
and
.IR function->requires_relaxation ,
they need not be set before any of the
.BR libnormalform_express (3),
.BR libnormalform_dnf (3),
and
.BR libnormalform_cnf (3)
functions are called.
.PP
.I function
must not be
.IR NULL .
.PP
The returned pointer shall either be
deallocated with the
.BR libnormalform_free (3)
function or be relinquished by being
used as part of another sentence.

.SH RETURN VALUE
Upon successful completion, the
.BR libnormalform_function ()
function returns an sentence object of
the function; otherwise, the function
returns
.I NULL
and sets
.I errno
to indicate the error.

.SH ERRORS
The
.BR libnormalform_function ()
function fails if:
.TP
.B ENOMEM
Insufficient memory was available to
create the sentence object.

.SH ATTRIBUTES
For an explanation of the terms used in this
section, see
.BR attributes (7)
and
.IR "info \(dq(libc)POSIX Safety Concepts\(dq" .
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR libnormalform_function ()
T}	Thread safety	MT-Safe
T{
.BR libnormalform_function ()
T}	Async-signal safety	AS-Unsafe heap
T{
.BR libnormalform_function ()
T}	Async-cancel safety	AC-Safe mem, AC-Unsafe heap
.TE

.SH SEE ALSO
.BR libnormalform (7),
.BR libnormalform_variable (3)