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Composition and Precedence

Composition uses two layers of rules:

  1. Each operation has a merge policy.
  2. Syntax 1.5.0 applies operations in declaration order.

Normative Precedence

Operation Same-shape field conflict Shape mismatch
@inherit Child value wins Child body wins
@use Imported source value wins Existing target body wins
Local block Applied at its source position Applied at its source position
@extend Merge using target shape policy Invalid incompatible extension
@override Replace complete existing target Replace complete existing target

For multiple @use declarations, each later import becomes the new source. Its same-shape values win against the accumulated target.

A field keeps the position of its first declaration. Later operations change its value, not its place, and fields that a later layer introduces are appended in declaration order. Resolved output therefore stays stable when an inherited or imported field is redefined.

The operation mode comes from the effective composed graph. A 1.5.0 source or ordered operation in inherited, imported, inline-composed, or extension-carried content enables declaration order for the whole graph. Inline @use declarations inside an @extend body are part of that graph. Lower-version entry files still resolve, while PS018 reports the source requirement and recommends an upgrade. Graphs without ordered sources retain legacy phase ordering.

Resolved Example

# base.prs
@meta { id: "base" syntax: "1.5.0" }
@standards {
  testing: ["Use Jest"]
  coverage: 80
}

# quality.prs
@meta { id: "quality" syntax: "1.5.0" }
@standards {
  coverage: 90
  review: ["Require approval"]
}

# project.prs
@meta { id: "project" syntax: "1.5.0" }
@inherit ./base
@use ./quality
@standards {
  local: ["Run smoke tests"]
}
@override standards.coverage { 95 }

Try in Playground

Resolved @standards:

testing: ["Use Jest"]
coverage: 95
review: ["Require approval"]
local: ["Run smoke tests"]

quality supplies coverage: 90 during import. Later @override replaces it with 95.

Enterprise Guidance

  • Keep one linear organizational base in @inherit.
  • Use @use for optional capabilities and shared fragments.
  • Put local blocks after imports when local policy should apply later.
  • Use @override when replacement intent must be explicit.
  • Validate resolved output, not only source files.
  • Pin remote imports and commit promptscript.lock.

See Execution Order for operation timing and Merge and Replacement for modification choices.