<errors of=…/>

Syntax

<errors of=@cellExpr/>
<errors of=@compound.field all/>
<errors of=@compound/>

of= takes a reactive expression pointing at a cell, a compound field, or a compound as a whole. The all attribute toggles full-array rendering (every error) vs. first-error-only (default).

Worked example

A signup form. Three fields, three validators, one <errors> per field. Zero manual error state. The validity surface is reactive, read-only, and updates as the user types.

<signup>
    <name  req length(>=2)> = <input type="text"/>
    <email req>             = <input type="email"/>
    <agree req>             = <input type="checkbox"/>
</>

<form onsubmit=submit()>
    <label>Name  <signup.name/></label>
    <errors of=@signup.name/>

    <label>Email <signup.email/></label>
    <errors of=@signup.email/>

    <label>Agree <signup.agree/></label>
    <errors of=@signup.agree/>

    <button type="submit" disabled=${!@signup.isValid}>Submit</button>

    <errors of=@signup all/>
</form>

Semantics

• Errors are enum tags, not strings. @signup.name.errors[0] is .Required or .LengthFailed(predicate) — consumers pattern-match on the tag. The ValidationError enum at SPEC §55.9 has one tag per predicate.
• Universal-core predicate vocabulary (14 predicates). Same word at compile site and runtime: req, is some, length(<rel-arg>), pattern, min, max, gt, lt, gte, lte, eq, neq, oneOf, notIn. Per SPEC §55.1.
• Three loci, same vocabulary. The same predicates fire on state-cell decls (reactive form validity), refinement-type expressions (compile-time + runtime boundary), and <schema> columns (additive to SQL-mirror DDL). Per Lock L4.
• 4-level error message resolution chain. (1) inline on decl (<name req:"Please enter your name">); (2) project-registered via registerMessages from scrml:data; (3) stdlib defaults (English); (4) match escape hatch (<match for=ValidationError>). Per SPEC §55.5.
• Cross-field validation via predicate args. <confirm req eq(@signup.password)> — no separate cross-field vocabulary. The dependency is tracked at the predicate-arg level (Lock L14).

Errors this feature can fire

• E-ERRORS-001 — <errors of=expr/> missing of= attribute
• E-ERRORS-002 — <errors> on a cell with no validators
• E-SYNTHESIZED-WRITE — write to read-only @x.isValid / .errors / .touched
• E-DERIVED-WITH-VALIDATORS — validators on const-derived cells (forbidden)
• E-VALIDATOR-CIRCULAR-DEP — predicate-arg cycle across cells

Edge cases

• The validity surface is read-only. Writing to @signup.isValid = true fires E-SYNTHESIZED-WRITE at compile time. To dismiss errors, fix the underlying cell value. To bypass validity entirely, the cell shouldn't have validators.
• Derived cells cannot carry validators. const <fullName req> = … fires E-DERIVED-WITH-VALIDATORS. Use a refinement-type predicate at the type level instead — derived cells are an expression, not user input.
• The compound rollup is short-circuit-friendly. @signup.isValid false-shortcircuits at the first invalid field. Useful for disabling submit buttons or gating server calls without walking every field manually.
• all attribute behaviour. Without all: <errors of=…/> renders the FIRST error only. With all: renders the entire array. The default favours minimal UI noise; all is for forms where the user benefits from seeing every blocker at once.

Related features

• req — required validator. The most common validator in scrml code.
• is some — distinct from req. is some checks existence ("" IS some); req checks meaningful value ("" fails req).
• registerMessages via scrml:data — project-level message catalog for the 4-level resolution chain.
• <schema> — third locus for the universal-core vocabulary. Schema columns can carry the same predicates.
• Learn: Validators — narrative walkthrough.

Availability

Specification

This page summarizes SPEC §55 (~26381-26869). The normative text lives at compiler/SPEC.md . When this page disagrees with SPEC.md, SPEC.md is authoritative.