call

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)#

call opens a channel endpoint and materializes the stream with an explicit conversion target.

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

# Exemplar: expression `call` with `channel ↦ string` materialization.
#
# Proves the conversion returns the echoed opener text as a `string` value.
# The runtime:echo backend echoes the opener back as a single string frame;
# `↦ string` 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)#

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

# =============================================================================
# call — `@ call '<route>'` serves a route from a Faber function.
# =============================================================================
#
# What this teaches:
#   • Serving a route — `@ call 'salutatio:saluta'` registers `saluta` as the
#     program's handler for that route; no host is needed for it
#   • The caller side is unchanged — `call 'salutatio:saluta' ("munde")` opens a
#     channel and `↦ string` 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 class to send several values
#
# See also: call, channel, conversion
# =============================================================================

@ call 'salutatio:saluta'
fn saluta(string name) → string {
    return "salve, " + name
}

main {
    const string responsum ← call 'salutatio:saluta' ("munde") ↦ string
    print 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: call, channel, recv, conversion
# =============================================================================

@ 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