调用

A call to a Faber-served route is a typed conversation channel<O, R>: the opener and every reply are checked against the handler.

Syntax: const channel<O, R> s ← call 'prefix:name' (o)

Category#

endpoint

Related#

• conversio

Examples#

radix/corpus/ad/sermo-conversio.fab (canonical · keyword)#

调用 opens a 通道 endpoint and materializes the stream with an explicit 转换 target.

# =============================================================================
# 调用 — 调用 opens a 通道 endpoint and materializes the stream with an explicit
# 转换 target.
# =============================================================================
#
# What this teaches:
#   • Endpoint materialization — `调用 'runtime:echo'(payload) ↦ 文本` opens a
#     通道 connection and converts the stream to a concrete type
#   • The `↦` materialization operator — directs how the inbound frame stream
#     is interpreted
#
# Common mistakes:
#   • confusing 调用 route syntax — the materialization target type must match the endpoint's actual return shape
#
# See also: 转换
# =============================================================================

# Exemplar: expression `调用` with `通道 ↦ 文本` materialization.
#
# Proves the 转换 returns the echoed opener text as a `文本` value.
# The runtime:echo backend echoes the opener back as a single 文本 frame;
# `↦ 文本` materializes it. The exemplar asserts equality.

main {
    const string t ← call 'runtime:echo' ("salve, munde") ↦ string
    assert t ≡ "salve, munde"
}

Expected output:

radix/corpus/ad/serve-plain.fab (canonical · annotation)#

@ 调用 serves a route from a Faber function; a caller ads the route and materializes the one reply frame.

# =============================================================================
# 调用 — `@ 调用 '<route>'` serves a route from a Faber function.
# =============================================================================
#
# What this teaches:
#   • Serving a route — `@ 调用 'salutatio:saluta'` registers `saluta` as the
#     program's handler for that route; no host is needed for it
#   • The caller side is unchanged — `调用 'salutatio:saluta' ("munde")` opens a
#     通道 and `↦ 文本` materializes the reply
#   • Plain return — a handler that returns one value answers one item frame,
#     then done
#
# Common mistakes:
#   • giving a handler two parameters — a handler takes zero or one opener;
#     pass a 类 to send several values
#
# See also: 调用, 通道, 转换
# =============================================================================

@ 调用 'salutatio:saluta'
函数 saluta(文本 名称) → 文本 {
    返回 "salve, " + 名称
}

入口 {
    常量 文本 responsum ← 调用 'salutatio:saluta' ("munde") ↦ 文本
    显示 responsum
}

Expected output:

salve, munde

radix/corpus/ad/serve-typed.fab (canonical · annotation)#

A call to a Faber-served route is a typed conversation channel<O, R>: the opener and every reply are checked against the handler.

# =============================================================================
# call — a conversation with a Faber handler is typed `channel<O, R>`.
# =============================================================================
#
# What this teaches:
#   • Typed conversation — when a Faber function serves the route, `call` has
#     type `channel<O, R>`: `O` is the handler's parameter, `R` each item back
#   • Inference — `const _ s ← call '…'` infers `channel<O, R>` from the route
#   • Dropping the types — a typed channel assigns to a bare `channel`, which
#     reads its frames as loose values again
#   • No opener — a handler without a parameter has `O = null`, and the call
#     passes no opener
#
# Common mistakes:
#   • materializing as a type other than `R` or `list<R>` — a compile error
#   • passing an opener of the wrong type — the handler's parameter decides
#   • a bare `channel` is `channel<value, value>`; host routes stay untyped
#
# See also: 调用, 通道, 接收, 转换
# =============================================================================

@ call 'numeri:twice'
fn twice(int n) → int {
    return n * 2
}

@ call 'salutatio:greeting'
fn greeting() → string {
    return "salve"
}

main {
    const _ s ← call 'numeri:twice' (21)
    const int doubled ← s ↦ int
    print doubled

    const channel<none, string> g ← call 'salutatio:greeting'
    print g ↦ string

    const channel<int, int> t ← call 'numeri:twice' (5)
    const channel loose ← t
    print loose ↦ int
}

Expected output:

42
salve
10