primus_quem

Dedicated total first-match expression: first live element of a source satisfying the owned ubi predicate, نوع_لاشيء for no-match and empty sources.

Aliases: primus quem

Syntax: primus_quem(<source>, ubi <binder> { <predicate> })

Category#

collection

Related#

• لاشيء

Examples#

radix/corpus/primus-quem/primus-quem.fab (canonical · concept)#

Dedicated total first-match expression: first live element of a source satisfying the owned ubi predicate, نوع_لاشيء for no-match and empty sources.

# =============================================================================
# primus_quem — dedicated total first-match selection over a bounded source.
# =============================================================================
#
# What this teaches:
#   • dedicated head — `primus_quem(source, ubi x { predicate })` is its own
#     expression (not a `اكسر`/`إذا` reuse and not a method call); the `ubi`
#     tail is owned by this head
#   • total evaluation — the predicate is evaluated for EVERY candidate مسار
#     (post-match lanes included); selection is dataflow first-live, never an
#     early exit
#   • `T ∪ نوع_لاشيء` — no-match and empty sources return `نوع_لاشيء`, never an error;
#     a predicate ERROR rides the error channel and is never converted to
#     `نوع_لاشيء`
#   • first-live — later live lanes never overwrite the first stored match
#     ([1.0, 5.0, 3.0] over `> 2.0` picks 5.0, not 3.0)
#   • declines — unbounded sources fail closed (SEM059
#     first_match_unbounded_source, causa not_bounded) and multi-axis `عند`
#     coordinates stay unsupported in v1 (SEM059
#     first_match_expression_unsupported); see primus-quem-decline.fab
#
# Common mistakes:
#   • expecting an index/value pair — v1 returns only `T ∪ نوع_لاشيء`; construct
#     the explicit pair yourself if you need the index
#   • expecting early exit — the predicate still runs after the first match
#
# See also: ubi, نوع_لاشيء, filtrata, primus
# =============================================================================

# Route T — array literal source: first live مسار over `> 0.0` is 1.0.
دالة elige_litteram() → كسر ∪ نوع_لاشيء {
    أعد primus_quem([1.0, -2.0, 3.0], ubi x { x > 0.0 })
}

# No-match — no live مسار yields نوع_لاشيء, never an error.
دالة elige_nullum() → كسر ∪ نوع_لاشيء {
    أعد primus_quem([1.0, 2.0], ubi x { x > 9.0 })
}

# Empty source — a statically zero-length array yields نوع_لاشيء.
دالة elige_vacuum(قائمة<f32> xs) → كسر ∪ نوع_لاشيء {
    أعد primus_quem(xs, ubi x { x > 0.0 })
}

# First-live — with matches at 5.0 and 3.0, the FIRST live مسار wins.
دالة elige_primum_viventem(قائمة<f32> xs) → كسر ∪ نوع_لاشيء {
    أعد primus_quem(xs, ubi x { x > 2.0 })
}

بداية {
    ثابت كسر ∪ نوع_لاشيء litteram ← elige_litteram()
    ثابت كسر ∪ نوع_لاشيء nullum ← elige_nullum()
    ثابت قائمة<f32> vacua_lista ← []
    ثابت كسر ∪ نوع_لاشيء فراغ ← elige_vacuum(vacua_lista)
    ثابت قائمة<f32> xs ← [1.0, 5.0, 3.0]
    ثابت كسر ∪ نوع_لاشيء primum ← elige_primum_viventem(xs)

    اعرض litteram
    اعرض nullum
    اعرض فراغ
    اعرض primum
}

Expected output:

1.0
nihil
nihil
5.0

radix/corpus/primus-quem/primus-quem-decline.fab (supporting · reject)#

primus_quem AIR decline rows: unbounded sources fail closed (not_bounded) and عند coordinates on first-match stay unsupported in v1.

# =============================================================================
# primus_quem decline — bounded sources only on the AIR مسار.
# =============================================================================
#
# Decline rows (reject reason in each comment):
#   1. unbounded source — an unbounded `قائمة` parameter has no static
#      extent; the AIR gate fails closed:
#      SEM059 first_match_unbounded_source (causa not_bounded)
#   2. عند coordinates — the multi-axis `عند [i]` form on the first-match
#      head stays unsupported in v1 (honest decline, not a silent pass):
#      SEM059 first_match_expression_unsupported
#
# Common mistakes:
#   • expecting an unbounded `قائمة` local to admit because its initializer
#      is a literal — the route classifier sees the unbounded path type
#   • expecting early-exit semantics to excuse the bound — admission needs
#      the static extent for the first-live mask, not an unroll
#
# See also: primus_quem, ubi, قائمة, عند
# =============================================================================

# 1. unbounded — قائمة parameter has no static extent, declines not_bounded
@ radix مسار "air"
دالة elige_infinita(قائمة<f32> xs) → كسر ∪ نوع_لاشيء {
    أعد primus_quem(xs, ubi v { v > 0.0 })
}

# 2. عند coordinates — multi-axis first-match stays unsupported in v1
@ radix مسار "air"
دالة elige_apud(tf32[4] a) → كسر ∪ نوع_لاشيء {
    أعد primus_quem(a عند [i], ubi v { v > 0.0 })
}

Expected: compilation rejects this example.