Function Invocation

Function Invocation

The primary way to call other functions in Wippy. Execute registered functions synchronously or asynchronously across processes, with full support for context propagation, security credentials, and timeouts. This module is central to building distributed applications where components need to communicate.

Loading

local funcs = require("funcs")

call

Calls a registered function synchronously. Use this when you need an immediate result and can wait for it.

local result, err = funcs.call("app.api:get_user", user_id)
if err then
    return nil, err
end
print(result.name)

Parameter	Type	Description
target	string	Function ID in format “namespace:name”
...args	any	Arguments passed to the function

Returns: result, error

The target string follows the pattern namespace:name where namespace identifies the module and name identifies the specific function.

async

Starts an async function call and returns immediately with a Future. Use this for long-running operations where you don’t want to block, or when you want to run multiple operations in parallel.

-- Start heavy computation without blocking
local future, err = funcs.async("app.process:analyze_data", large_dataset)
if err then
    return nil, err
end

-- Do other work while computation runs...

-- Wait for result when ready
local ch = future:response()
local payload, ok = ch:receive()
if ok then
    local result = payload:data()
end

Parameter	Type	Description
target	string	Function ID in format “namespace:name”
...args	any	Arguments passed to the function

Returns: Future, error

new

Creates a new Executor for building function calls with custom context. Use this when you need to propagate request context, set security credentials, or configure timeouts.

local exec = funcs.new()

Returns: Executor

Executor

Builder for function calls with custom context options. Methods return new Executor instances (immutable chaining), so you can reuse a base configuration.

with_context

Adds context values that will be available to the called function. Use this to propagate request-scoped data like trace IDs, user sessions, or feature flags.

-- Propagate request context to downstream services
local exec = funcs.new():with_context({
    request_id = ctx.get("request_id"),
    feature_flags = {dark_mode = true}
})

local user, err = exec:call("app.api:get_user", user_id)

Parameter	Type	Description
values	table	Key-value pairs to add to context

Returns: Executor, error

with_actor

Sets the security actor for authorization checks in the called function. Use this when calling a function on behalf of a specific user.

local security = require("security")
local actor = security.actor()  -- Get current user's actor

-- Call admin function with user's credentials
local exec = funcs.new():with_actor(actor)
local result, err = exec:call("app.admin:delete_record", record_id)
if err and err:kind() == errors.PERMISSION_DENIED then
    return nil, errors.new("PERMISSION_DENIED", "User cannot delete records")
end

Parameter	Type	Description
actor	Actor	Security actor (from security module)

Returns: Executor, error

with_scope

Sets the security scope for called functions. Scopes define the permissions available for the call.

local security = require("security")
local scope = security.new_scope()

local exec = funcs.new():with_scope(scope)

Parameter	Type	Description
scope	Scope	Security scope (from security module)

Returns: Executor, error

with_options

Sets call options like timeout and priority. Use this for operations that need time limits.

-- Set a 5 second timeout for external API call
local exec = funcs.new():with_options({timeout = 5000})
local result, err = exec:call("app.external:fetch_data", query)
if err then
    -- Handle timeout or other error
end

Parameter	Type	Description
options	table	Implementation-specific options

Returns: Executor, error

call / async

Executor versions of call and async that use the configured context.

-- Build reusable executor with context
local exec = funcs.new()
    :with_context({trace_id = "abc-123"})
    :with_options({timeout = 10000})

-- Make multiple calls with same context
local users, _ = exec:call("app.api:list_users")
local posts, _ = exec:call("app.api:list_posts")

Future

Returned by async() calls. Represents an in-progress async operation.

response / channel

Returns the underlying channel for receiving the result.

local future, _ = funcs.async("app.api:slow_operation", data)
local ch = future:response()  -- or future:channel()

local result = channel.select {
    ch:case_receive(),
    timeout:case_receive()
}

Returns: Channel

is_complete

Non-blocking check if the future has completed.

while not future:is_complete() do
    -- do other work
    time.sleep("100ms")
end
local result, err = future:result()

Returns: boolean

is_canceled

Returns true if cancel() was called on this future.

if future:is_canceled() then
    print("Operation was canceled")
end

Returns: boolean

result

Returns the cached result if complete, or nil if still pending.

local value, err = future:result()
if err then
    print("Failed:", err:message())
elseif value then
    print("Got:", value:data())
end

Returns: Payload|nil, error|nil

error

Returns the error if the future failed.

local err, has_error = future:error()
if has_error then
    print("Error kind:", err:kind())
end

Returns: error|nil, boolean

cancel

Cancels the async operation.

future:cancel()

Returns: boolean, error

Parallel Operations

Run multiple operations concurrently using async and channel.select.

-- Start multiple operations in parallel
local f1, _ = funcs.async("app.api:get_user", user_id)
local f2, _ = funcs.async("app.api:get_orders", user_id)
local f3, _ = funcs.async("app.api:get_preferences", user_id)

-- Wait for all to complete using channels
local user_ch = f1:channel()
local orders_ch = f2:channel()
local prefs_ch = f3:channel()

local results = {}
for i = 1, 3 do
    local r = channel.select {
        user_ch:case_receive(),
        orders_ch:case_receive(),
        prefs_ch:case_receive()
    }
    if r.channel == user_ch then
        results.user = r.value:data()
    elseif r.channel == orders_ch then
        results.orders = r.value:data()
    else
        results.prefs = r.value:data()
    end
end

Permissions

Function operations are subject to security policy evaluation.

Action	Resource	Description
funcs.call	Function ID	Call a specific function
funcs.context	context	Use with_context() to set custom context
funcs.security	security	Use with_actor() or with_scope()

Errors

Condition	Kind	Retryable
Target empty	errors.INVALID	no
Namespace missing	errors.INVALID	no
Name missing	errors.INVALID	no
Permission denied	errors.PERMISSION_DENIED	no
Subscribe failed	errors.INTERNAL	no
Function error	varies	varies

See Error Handling for working with errors.