From 54a545359ea9b8de8da66d1e1e8f6b4b5e396f75 Mon Sep 17 00:00:00 2001
From: Thomas Mailund <mailund@birc.au.dk>
Date: Mon, 25 Feb 2019 15:36:53 +0100
Subject: [PATCH] capturing closures

---
 NAMESPACE               |  1 +
 R/loop-transformation.R | 19 +++++++++++++++++++
 man/capture_closure.Rd  | 15 +++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 man/capture_closure.Rd

diff --git a/NAMESPACE b/NAMESPACE
index 87e5289..5b59f6e 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -2,5 +2,6 @@
 
 export(can_loop_transform)
 export(can_loop_transform_)
+export(capture_closure)
 export(loop_transform)
 import(foolbox)
diff --git a/R/loop-transformation.R b/R/loop-transformation.R
index 280e409..a4644a0 100644
--- a/R/loop-transformation.R
+++ b/R/loop-transformation.R
@@ -106,6 +106,10 @@ try_loop_transform <- function(fun) {
         call_arguments <- rlang::call_args(expr)
         fun_call_allowed <- topdown
 
+        if (call_name == "function") {
+            skip(expr) # whatever we do when defining a functio won't be executed here
+        }
+
         if (call_name == fun_name) {
             if (!fun_call_allowed) {
                 warn_msg <- simpleWarning(
@@ -389,3 +393,18 @@ loop_transform <- function(fun, byte_compile = TRUE, set_srcref = TRUE) {
 
     result
 }
+
+#' Captures the closure in a function environment
+#'
+#' This is necessary to implement continuation-passing-style
+#' tail-recursion.
+#'
+#' @param .func The function to capture a closure for.
+#'
+#' @export
+capture_closure <- function(.func) {
+    captured_env <- rlang::env_clone(rlang::caller_env())
+    environment(.func) <- captured_env
+    .func
+}
+
diff --git a/man/capture_closure.Rd b/man/capture_closure.Rd
new file mode 100644
index 0000000..bfe6325
--- /dev/null
+++ b/man/capture_closure.Rd
@@ -0,0 +1,15 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/loop-transformation.R
+\name{capture_closure}
+\alias{capture_closure}
+\title{Captures the closure in a function environment}
+\usage{
+capture_closure(.func)
+}
+\arguments{
+\item{.func}{The function to capture a closure for.}
+}
+\description{
+This is necessary to implement continuation-passing-style
+tail-recursion.
+}