Add context()

src/context.luau

@@ -0,0 +1,75 @@
+if not game then script = require "test/relative-string" end
+
+local throw = require(script.Parent.throw)
+local graph = require(script.Parent.graph)
+type Node<T> = graph.Node<T>
+local create_node = graph.create_node
+local get_scope = graph.get_scope
+local push_scope = graph.push_scope
+local pop_scope = graph.pop_scope
+local set_context = graph.set_context
+
+export type Context<T> = (() -> T) & ((T, () -> ()) -> ())
+
+local nil_symbol = newproxy()
+local count = 0
+
+local function context<T>(...: T): Context<T>
+    count += 1
+    local id = count
+
+    local has_default = select("#", ...) > 0
+    local default_value = ...
+
+    return function(...)
+        local scope: Node<unknown>? | false = get_scope()
+
+        if select("#", ...) == 0 then -- get
+            while scope do
+                local ctx = scope.context
+    
+                if not ctx then
+                    scope = scope.owner
+                    continue
+                end
+
+                local value = (ctx :: { unknown })[id]
+
+                if value == nil then
+                    scope = scope.owner
+                    continue
+                end
+                
+                return (if value ~= nil_symbol then value else nil) :: T
+            end
+
+            if has_default ~= nil then
+                return default_value
+            else
+                throw("attempt to get context when no context is set and no default context is set")
+            end
+        else -- set
+            if not scope then return throw("attempt to set context outside of a vide scope") end
+
+            local value, component = ...
+            
+            local new_scope = create_node(scope, false, false)
+            set_context(new_scope, id, if value == nil then nil_symbol else value)
+
+            push_scope(new_scope)
+
+            local function efn(err: string) return debug.traceback(err, 3) end
+            local ok, result = xpcall(component, efn)
+
+            pop_scope()
+
+            if not ok then
+                throw(`error while running context:\n\n{result}`)
+            end
+        end
+
+        return nil :: any
+    end
+end
+
+return context

src/graph.luau

@@ -13,6 +13,8 @@ export type Node<T> =  {
     effect:  ((T) -> T) | false,
     cleanups: { () -> () } | false,
 
+    context: { [number]: unknown } | false,
+
     owned: { Node<T> } | false,
     owner: Node<T> | false,
 
@@ -241,6 +243,8 @@ local function create_node<T>(owner: false | Node<any>, effect: false | (T) -> T
         effect = effect,
         cleanups = false,
 
+        context = false,
+
         owner = owner,
         owned = false,
 
@@ -266,6 +270,14 @@ local function get_children<T>(node: Node<T>): { Node<unknown> }
     return { unpack(node) } :: { Node<any> }
 end
 
+local function set_context<T>(node: Node<T>, key: number, value: unknown)
+    if node.context then
+        node.context[key] = value
+    else
+        node.context = { [key] = value }
+    end
+end
+
 return table.freeze {
     push_scope = push_scope,
     pop_scope = pop_scope,
@@ -283,5 +295,6 @@ return table.freeze {
     get_children = get_children,
     flush_update_queue = flush_update_queue,
     get_update_queue_length = get_update_queue_length,
+    set_context = set_context,
     scopes = scopes
 }

src/init.luau

@@ -16,6 +16,7 @@ local cleanup = require(script.cleanup)
 local untrack = require(script.untrack)
 local read = require(script.read)
 local batch = require(script.batch)
+local context = require(script.context)
 local switch = require(script.switch)
 local show = require(script.show)
 local indexes, values = require(script.maps)()
@@ -26,6 +27,9 @@ local throw = require(script.throw)
 local flags = require(script.flags)
 
 export type Source<T> = source.Source<T>
+export type source<T> = Source<T>
+export type Context<T> = context.Context<T>
+export type context<T> = Context<T>
 
 local function step(dt: number)
     if game then
@@ -63,6 +67,7 @@ local vide = {
     untrack = untrack,
     read = read,
     batch = batch,
+    context = context,
 
     -- animations
     spring = spring,