Errors with formulating logical statements are sometimes caught by the calculus module: this section collects and issues such errors as tidy Inform problems.

§1. The :calculus group of tests for inform7 generates all of the problems below.

define PROBLEM_CALCULUS_CALLBACK CalculusProblems::issue_problem

void CalculusProblems::issue_problem(int err_no, parse_node *spec, wording W,
    kind *K1, kind *K2, binary_predicate *bp, tc_problem_kit *tck) {
    switch(err_no) {
        case BareKindVariable_CALCERROR:
            Problems::quote_source(1, current_sentence);
            StandardProblems::handmade_problem(Task::syntax_tree(), _p_(PM_BareKindVariable));
            Problems::issue_problem_segment(
                "The sentence %1 seems to use a kind variable by its letter "
                "alone in the context of a noun, which Inform doesn't allow. "
                "It's fine to say 'if the noun is a K', for example, but "
                "not 'if K is number'. By putting 'a' or 'an' in front of the "
                "kind variable, you make clear that I'm supposed to perform "
                "matching against a description.");
            Problems::issue_problem_end();
            break;
        case ConstantFailed_CALCERROR:
            Problems::quote_source(1, current_sentence);
            Problems::quote_wording(2, Node::get_text(spec));
            StandardProblems::handmade_problem(Task::syntax_tree(), _p_(BelievedImpossible));
            Problems::issue_problem_segment(
                "The sentence %1 seems to contain a value '%2' which I can't make "
                "any sense of.");
            Problems::issue_problem_end();
            break;
        case UnaryMisapplied_CALCERROR:
            Problems::quote_wording(4, W);
            Problems::quote_kind(5, K1);
            StandardProblems::tcp_problem(_p_(PM_AdjectiveMisapplied), tck,
                "that seems to involve applying the adjective '%4' to %5 - and I "
                "have no definition of it which would apply in that situation. "
                "(Try looking it up in the Lexicon part of the Phrasebook index "
                "to see what definition(s) '%4' has.)");
            break;
        case ComparisonFailed_CALCERROR:
            Problems::quote_kind(4, K1);
            Problems::quote_kind(5, K2);
            char *msg;
            if (((Kinds::eq(K1, K_time)) && (Kinds::eq(K2, K_time_period))) ||
                ((Kinds::eq(K2, K_time)) && (Kinds::eq(K1, K_time_period))))
                msg = "that would mean comparing two kinds of value which cannot mix - "
                    "%4 and %5 - so this must be incorrect. Note that 'time period', "
                    "introduced in Inform in 2024, holds values like '10 minutes', "
                    "and is not the same kind as 'time', which is for times of day "
                    "like '6:12 PM'. (Before 2024, the same kind was used for both.)";
            else
                msg = "that would mean comparing two kinds of value which cannot mix - "
                    "%4 and %5 - so this must be incorrect.";
            StandardProblems::tcp_problem(_p_(PM_ComparisonFailed), tck, msg);
            break;
        case BadUniversal1_CALCERROR:
            Problems::quote_kind(4, K1);
            StandardProblems::tcp_problem(_p_(PM_BadUniversal1), tck,
                "that asks whether something relates something, and in Inform 'to relate' "
                "means that a particular relation applies between two things. Here, though, "
                "we have %4 rather than the name of a relation.");
            break;
        case BadUniversal2_CALCERROR:
            Problems::quote_kind(4, K1);
            StandardProblems::tcp_problem(_p_(BelievedImpossible), tck,
                "that asks whether something relates something, and in Inform 'to relate' "
                "means that a particular relation applies between two things. Here, though, "
                "we have %4 rather than the combination of the two things.");
            break;
        case BinaryMisapplied1_CALCERROR:
            Problems::quote_kind(4, K1);
            Problems::quote_kind(5, K2);
            Problems::quote_relation(6, bp);
            StandardProblems::tcp_problem(_p_(PM_TypeCheckBP2a), tck,
                "that doesn't work because you use %6 with %4 instead of %5.");
            break;
        case BinaryMisapplied2_CALCERROR:
            Problems::quote_kind(4, K1);
            Problems::quote_kind(5, K2);
            Problems::quote_relation(6, bp);
            StandardProblems::tcp_problem(_p_(PM_TypeCheckBP2), tck,
                "that would mean applying %6 to kinds of value which do not "
                "fit - %4 and %5 - so this must be incorrect.");
            break;
        case KindMismatch_CALCERROR:
            Problems::quote_kind(4, K1);
            Problems::quote_kind(5, K2);
            StandardProblems::tcp_problem(_p_(PM_TypeCheckKind), tck,
                "%4 cannot be %5, so this must be incorrect.");
            break;
        default:
            internal_error("unknown calculus error");
    }
}