Handles parentheses in simplification

This addresses #5.

R/simplify.R

@@ -99,6 +99,12 @@ simplify_call <- function(expr) {
 
   if (expr[[1]] == as.name("^")) return(simplify_exponentiation(expr[[2]], expr[[3]]))
 
+  if (expr[[1]] == as.name("(")) {
+    subexpr <- simplify_expr(expr[[2]])
+    if (is.atomic(subexpr) || is.name(subexpr)) return(subexpr)
+    else return(call("(", subexpr))
+  }
+
   if (as.character(expr[[1]]) %in% .simplify_built_in_functions) return(simplify_built_in_function(expr))
 
   stop(paste0("Unexpected call ", deparse(expr)))

tests/testthat/test-simpification.R

@@ -49,6 +49,9 @@ test_that("we can do some simplifications when there are variables involved", {
   expect_equal(simplify_expr(quote(x / x)), quote(x / x)) # we probably want to simplify this...
 
   expect_equal(simplify_expr(quote(x ^ y)), quote(x ^ y))
+
+  expect_equal(simplify_expr(quote(2*(x + 0))), quote(2*x))
+  expect_equal(simplify_expr(quote(2*(x + y))), quote(2*(x + y)))
 })
 
 test_that("we can handle some simple functions", {