lang: interfaces: API changes for lambdas

Co-authored-by: Samuel Gélineau <gelisam@gmail.com>

lang/interfaces/ast.go

@@ -107,7 +107,7 @@ type Expr interface {
 	Ordering(map[string]Node) (*pgraph.Graph, map[Node]string, error)
 
 	// SetScope sets the scope here and propagates it downwards.
-	SetScope(*Scope) error
+	SetScope(*Scope, map[string]Expr) error
 
 	// SetType sets the type definitively, and errors if it is incompatible.
 	SetType(*types.Type) error
@@ -122,8 +122,9 @@ type Expr interface {
 	Unify() ([]Invariant, error)
 
 	// Graph returns the reactive function graph expressed by this node. It
-	// also returns the function for this node.
-	Graph() (*pgraph.Graph, Func, error)
+	// takes in the environment of any functions in scope. It also returns
+	// the function for this node.
+	Graph(env map[string]Func) (*pgraph.Graph, Func, error)
 
 	// SetValue stores the result of the last computation of this expression
 	// node.

lang/interfaces/structs.go

@@ -76,7 +76,7 @@ func (obj *ExprAny) Ordering(produces map[string]Node) (*pgraph.Graph, map[Node]
 
 // SetScope does nothing for this struct, because it has no child nodes, and it
 // does not need to know about the parent scope.
-func (obj *ExprAny) SetScope(*Scope) error { return nil }
+func (obj *ExprAny) SetScope(*Scope, map[string]Expr) error { return nil }
 
 // SetType is used to set the type of this expression once it is known. This
 // usually happens during type unification, but it can also happen during
@@ -145,7 +145,7 @@ func (obj *ExprAny) Func() (Func, error) {
 // that fulfill the Stmt interface do not produces vertices, where as their
 // children might. This returns a graph with a single vertex (itself) in it, and
 // the edges from all of the child graphs to this.
-func (obj *ExprAny) Graph() (*pgraph.Graph, Func, error) {
+func (obj *ExprAny) Graph(env map[string]Func) (*pgraph.Graph, Func, error) {
 	graph, err := pgraph.NewGraph("any")
 	if err != nil {
 		return nil, nil, err