rules.hpp File Reference

x-rules read into RuleExpr trees, translated into the UI document's expression language (expr/1) and evaluated by its one evaluator, three-valued and exactly. More...

#include <algorithm>
#include <array>
#include <cstddef>
#include <cstdint>
#include <expected>
#include <functional>
#include <limits>
#include <optional>
#include <span>
#include <string>
#include <string_view>
#include <utility>
#include <vector>
#include "../../render/locale_format.hpp"
#include "../../ui/expression.hpp"
#include "../../ui/value.hpp"
#include "../../util/rational.hpp"
#include "detail/text.hpp"

Go to the source code of this file.

Classes
struct	morph::forms::SchemaError
	Why a schema does not read as a form: where, and why. More...
struct	morph::forms::RuleOperand
	What a rule reads of one field. More...
class	morph::forms::RuleExpr
	One x-rules entry, or a condition inside one, and its translation into expr/1. More...

Typedefs
using	morph::forms::RuleLookup = std::function<RuleOperand(std::string_view field)>
	Reads one field by wire name, for a rule. The session's lookup is tracked, so a verdict computed inside a reactive computation recomputes when a field it read changes.

Enumerations
enum class	morph::forms::Tri : std::uint8_t { False , True , Unknown }
	A three-valued verdict: a half-typed form has fields with no value yet, so a rule can be undecided. More...

Functions
constexpr Tri	morph::forms::triNot (Tri value) noexcept
	Kleene negation.
Tri	morph::forms::gatingVerdict (std::span< RuleExpr const > rules, RuleLookup const &lookup)
	Whether the gating rules let the form submit.
Tri	morph::forms::visibleVerdict (std::span< RuleExpr const > rules, std::string_view field, RuleLookup const &lookup)
	Whether field is shown: hidden as soon as one visibleWhen naming it is false.
Tri	morph::forms::readonlyVerdict (std::span< RuleExpr const > rules, std::string_view field, RuleLookup const &lookup)
	Whether field is frozen: as soon as one readonlyWhen naming it is true.
Tri	morph::forms::requiredVerdict (std::span< RuleExpr const > rules, std::string_view field, RuleLookup const &lookup)
	Whether field is required by a rule: as soon as one requiredWhen naming it is true.

Detailed Description

x-rules read into RuleExpr trees, translated into the UI document's expression language (expr/1) and evaluated by its one evaluator, three-valued and exactly.

Specified in docs/spec/forms/engine.md, "Rules".

Definition in file rules.hpp.

Typedef Documentation

RuleLookup

using morph::forms::RuleLookup = std::function<RuleOperand(std::string_view field)>

Reads one field by wire name, for a rule. The session's lookup is tracked, so a verdict computed inside a reactive computation recomputes when a field it read changes.

Definition at line 84 of file rules.hpp.

Enumeration Type Documentation

Tri

enum class morph::forms::Tri : std::uint8_t

strong

A three-valued verdict: a half-typed form has fields with no value yet, so a rule can be undecided.

Enumerator
False	Definitely does not hold.
True	Definitely holds.
Unknown	Cannot be decided: an operand does not encode, or the kind is not one this engine knows.

Definition at line 46 of file rules.hpp.

Function Documentation

triNot()

Tri morph::forms::triNot ( Tri value )

nodiscardconstexprnoexcept

Kleene negation.

Parameters

value

The verdict.

Returns

True for False, False for True, Unknown for Unknown.

Definition at line 55 of file rules.hpp.

gatingVerdict()

Tri morph::forms::gatingVerdict ( std::span< RuleExpr const > rules, RuleLookup const & lookup )

inlinenodiscard

Whether the gating rules let the form submit.

Only a False rule blocks: an Unknown one is waiting on a field that is required or does not encode, and that field blocks readiness itself; and a rule kind this engine does not know must not lock an older client out of a newer server's forms.

Parameters

rules	The rules.
lookup	Reads each operand.

Returns

False when some gating rule is false, Unknown when none is false and some is undecided, else True.

Definition at line 743 of file rules.hpp.

visibleVerdict()

Tri morph::forms::visibleVerdict ( std::span< RuleExpr const > rules, std::string_view field, RuleLookup const & lookup )

inlinenodiscard

Whether field is shown: hidden as soon as one visibleWhen naming it is false.

Parameters

rules	The rules.
field	The wire name.
lookup	Reads each operand.

Returns

False when hidden; Unknown presents as shown.

Definition at line 798 of file rules.hpp.

readonlyVerdict()

Tri morph::forms::readonlyVerdict ( std::span< RuleExpr const > rules, std::string_view field, RuleLookup const & lookup )

inlinenodiscard

Whether field is frozen: as soon as one readonlyWhen naming it is true.

Parameters

rules	The rules.
field	The wire name.
lookup	Reads each operand.

Returns

True when frozen; Unknown presents as editable.

Definition at line 808 of file rules.hpp.

requiredVerdict()

Tri morph::forms::requiredVerdict ( std::span< RuleExpr const > rules, std::string_view field, RuleLookup const & lookup )

inlinenodiscard

Whether field is required by a rule: as soon as one requiredWhen naming it is true.

Parameters

rules	The rules.
field	The wire name.
lookup	Reads each operand.

Returns

True when required; Unknown presents as not required.

Definition at line 818 of file rules.hpp.