Error taxonomy and recipes

Functions for lowering and rendering boundary schema failures.

Lowers a parse failure. Parsing failures never become constraint violations. ParseError.MissingValue "int" |> SchemaError.ofParseError

Primitive parse failures returned by Parse helpers.

The input was missing for the target primitive type.

Renders a schema error as an English sentence. Constraint violations delegate to Violation.render, so there is one rendering catalogue. SchemaError.render (SchemaError.InvalidFormat "int") // "Expected int format."

Schema input, checking, and contextual rule failures attached to diagnostics paths. The parse/check axis is the organising split. Parsing cases mean the input could not be read as the declared type at all; Violation means it was read and then failed its constraint. Constraint failures are never lowered into a parse-shaped case, because a lowering that discards the atom forces consumers back to reconstructing constraint identity from strings.

The input could not be read as the named target type.

Creates, executes, composes, and inspects constraints.

Runs a constraint, returning why the value failed. let retryCount = Constraint.between 0 10 42 |> Constraint.check retryCount |> Result.mapError Violation.render

Requires text to match Reified's pragmatic email shape, ^[^@]+@[^@]+$. let contact : Constraint<string> = Constraint.email

Apply a function to a value, the value being on the left, the function on the right The argument. The function. The function result. let doubleIt x = x * 2 3 |> doubleIt // Evaluates to 6

Fail-fast helpers over the standard F# Result type.

Maps the error value of a result.

Inspects, traverses, and renders violations.

Renders a violation as an English sentence fragment with no trailing punctuation, keeping conjunction and alternative groups distinct. Violation.render (Atomic (Expected (PresenceAtom Present, None))) // "value must be present"

Renders localized messages for one document context and attribute. Immutable: build one at the composition root and derive scoped copies with context and attribute. A renderer holds no violation and a violation holds no renderer. Context arrives here, at the rendering edge, which is what keeps Violation path-free, closure-free comparable data. context appends a document, model, form, or component segment. attribute replaces the whole attribute with one segment, so a form-scoped renderer is safe to reuse for sibling fields without leaking the previous field's noun.

One schema failure and its complete structural location.

The schema failure.

Schema input, checking, and contextual rule failures attached to diagnostics paths. The parse/check axis is the organising split. Parsing cases mean the input could not be read as the declared type at all; Violation means it was read and then failed its constraint. Constraint failures are never lowered into a parse-shaped case, because a lowering that discards the atom forces consumers back to reconstructing constraint identity from strings.

The value was read successfully and then failed its constraint.

Inspects, traverses, and renders violations.

Renders a violation as a localized predicate, with no attribute noun. Use this where a label already names the field — a form row, or a Schema result whose returned path identifies it. Conjunctions and alternatives join through the contextual constraint.group.* patterns; an actual value, when the violation carries one, is composed in through constraint.actual. violation |> Violation.message (renderer |> Renderer.context "signup" |> Renderer.attribute "name") // "must be at least 13, but was 11"

Functions for lowering and rendering boundary schema failures.

Renders a schema error as an English sentence. Constraint violations delegate to Violation.render, so there is one rendering catalogue. SchemaError.render (SchemaError.InvalidFormat "int") // "Expected int format."

Functions for building and formatting schema error paths.

Formats a path with dot-separated keys and bracketed indexes.

The location of the failure.

Structural equality The first parameter. The second parameter. The result of the comparison. 5 = 5 // Evaluates to true 5 = 6 // Evaluates to false [1; 2] = [1; 2] // Evaluates to true (1, 5) = (1, 6) // Evaluates to false

The concise schema-definition vocabulary: the record computation expression, its field and constructor forms, and the collection-schema operations. Optional and opt-in, in the same shape as Reified.DataDSL and Reified.ConstraintDSL: open Reified.Schema for Schema, then open Reified.SchemaDSL for this vocabulary. There is no constraint catalogue here. One Constraint vocabulary serves direct checking, refinement, and Schema, so a field block reaches for Constraint.email or an opened Reified.ConstraintDSL exactly as standalone code does. Boundary supply is Schema-owned and stays here as mustSupply and mayOmit.

Constraint constructors usable without the Constraint. prefix inside a module that declares value rules. Optional vocabulary, not another abstraction. Opening it makes a declaration read minLength 3 instead of Constraint.minLength 3; everything here is the same value the qualified name returns. Some constructors are deliberately left out because they shadow names the same validation code is likely to need in scope: contains, distinct, all, any, length, and between shadow core F# operations. Reach for those as Constraint.contains, Constraint.all, and so on, even inside a module that has opened this DSL. Constraint execution (Constraint.satisfies, Constraint.check, Constraint.guard) is likewise always qualified: ConstraintDSL declares constraints, Constraint.* executes and inspects them. orError and mapError are structural adapters matching the corresponding Result operations. They let a constraint pipeline retain its input and finish with the application's error type without adding an Reified.Result dependency. module SignupRules = open Reified.ConstraintDSL let age : Constraint<int> = atLeast 13 let contact : Constraint<string> = Constraint.all [ present; email ] let requireContact value = value |> Constraint.guard contact |> orError EmailRequired

An abbreviation for the CLI type . Basic Types

An abbreviation for the CLI type . Basic Types

A schema parse result that retains its original structured input.

Helper type for error handling without exceptions. Choices and Results

The type of immutable singly-linked lists. See the module for further operations related to lists. Use the constructors [] and :: (infix) to create values of this type, or the notation [1; 2; 3]. Use the values in the List module to manipulate values of this type, or pattern match against the values directly. See also F# Language Guide - Lists.

The parsed model or accumulated schema failures.

Represents an OK or a Successful result. The code succeeded with a value of 'T.

Represents an Error or a Failure. The code failed with a value of 'TError representing what went wrong.

Apply a function to a value, the value being on the left, the function on the right The argument. The function. The function result. let doubleIt x = x * 2 3 |> doubleIt // Evaluates to 6

Functions for inspecting and rendering accumulated schema failures.

Returns failures in deterministic path order.

Contains operations for working with values of type . Operations for collections such as lists, arrays, sets, maps and sequences. See also F# Collection Types in the F# Language Guide.

Builds a new collection whose elements are the results of applying the given function to each of the elements of the collection. The function to transform elements from the input list. The input list. The list of transformed elements. let inputs = [ "a"; "bbb"; "cc" ] inputs |> List.map (fun x -> x.Length) Evaluates to [ 1; 3; 2 ]

Functions for building and formatting schema error paths.

Formats a path with dot-separated keys and bracketed indexes.

The location of the failure.

Functions for lowering and rendering boundary schema failures.

Renders a schema error as an English sentence. Constraint violations delegate to Violation.render, so there is one rendering catalogue. SchemaError.render (SchemaError.InvalidFormat "int") // "Expected int format."

The schema failure.