diff --git a/agda/Parse.agda b/agda/Parse.agda
index c19621c..2e8515c 100644
--- a/agda/Parse.agda
+++ b/agda/Parse.agda
@@ -119,14 +119,29 @@ takeOper s with takeCons opers s
 -- ...                                   | emit (just (Oper o)) rem₂ = emit↓ (Oper o) rem₂
 -- ...                                   | emit _ rem₂ = emit↑ rem
 
+takeAlt : { R : Set } → ( List Char → Result R ) → ( List Char → Result R ) → List Char → Result R
+
+takeGroup : { G : Set } → ( List Char → Result G ) → List Char → Result G
+
 takeBin : List Char → Result BinExpr
-takeBin s with takeNat (ignoreCons skips s)
+takeBin s with (takeAlt takeNat (takeGroup takeNat)) (ignoreCons skips s)
 ...          | emit nothing rem₁ = emit↑ s
 ...          | emit (just res₁) rem₁ with takeOper (ignoreCons skips rem₁)
 ...                                     | emit nothing rem₂ = emit↑ rem₁
-...                                     | emit (just oper) rem₂ with takeNat (ignoreCons skips rem₂)
+...                                     | emit (just oper) rem₂ with (takeAlt takeNat (takeGroup takeNat)) (ignoreCons skips rem₂)
 ...                                                                | emit nothing rem₃ = emit↑ rem₁
 ...                                                                | emit (just res₃) rem₃ = emit↓ (bin oper (Digit res₁) (Digit res₃)) rem₃
 
+takeGroup f s with takeCons ('(' ∷ []) s
+...              | emit _ rem with f rem
+...                              | emit g rem₂ with takeCons (')' ∷ []) rem₂
+...                                               | emit _ rem₃ = emit g rem₃
+
+takeAlt a b s with a s
+...              | emit (just r) rem = emit↓ r rem
+...              | emit nothing rem with b s
+...                                    | emit (just r) rem = emit↓ r rem
+...                                    | emit nothing rem = emit↑ s
+
 takeLine : List Char → List (Result BinExpr)
-takeLine s = map takeBin (map reverse (reverse (split (';' ∷ []) s)))
+takeLine s = map (takeAlt takeBin (takeGroup takeBin)) (map reverse (reverse (split (';' ∷ []) s)))
diff --git a/typescript/Parse.ts b/typescript/Parse.ts
index e542547..d3c6103 100644
--- a/typescript/Parse.ts
+++ b/typescript/Parse.ts
@@ -253,13 +253,16 @@ export function takeOper(s: ReadonlyArray<string>): Result<Token> {
  * attempt to take a binary expression from a stream.
  */
 export function takeBin(s: ReadonlyArray<string>): Result<BinExpr> {
-  const lhs = takeNat(ignoreCons(SKIPS, s));
+  const takeAltNatGroup: (s: ReadonlyArray<string>) => Result<number> =
+    (takeAlt<number>).bind(nothing(), takeNat, (takeGroup<number>).bind(nothing(), takeNat));
+
+  const lhs = takeAltNatGroup(ignoreCons(SKIPS, s));
 
   if (isCont(lhs)) {
     const oper = takeOper(ignoreCons(SKIPS, remain(lhs)));
 
     if (isCont(oper)) {
-      const rhs = takeNat(ignoreCons(SKIPS, remain(oper)));
+      const rhs = takeAltNatGroup(ignoreCons(SKIPS, remain(oper)));
 
       if (isCont(rhs)) {
         return emitCont(bin(result(oper), digit(result(lhs)), digit(result(rhs))), remain(rhs));
@@ -270,9 +273,34 @@ export function takeBin(s: ReadonlyArray<string>): Result<BinExpr> {
   return emitBack(s);
 }
 
+export function takeGroup<T>(f: (s: ReadonlyArray<string>) => Result<T>, s: ReadonlyArray<string>): Result<T> {
+  const a = takeCons(['('], s);
+  const b = f(remain(a));
+  const c = takeCons([')'], remain(b));
+
+  return emit(b.res, remain(c));
+}
+
+export function takeAlt<T>(a: (s: ReadonlyArray<string>) => Result<T>, b: (s: ReadonlyArray<string>) => Result<T>, s: ReadonlyArray<string>): Result<T> {
+  const ra = a(s);
+  if (isCont(ra)) {
+    return ra;
+  }
+
+  const rb = b(s);
+  if (isCont(rb)) {
+    return rb;
+  }
+
+  return emitBack(s);
+}
+
 /**
  * split a string into expressions and parse them
  */
 export function takeLine(c: ReadonlyArray<string>): ReadonlyArray<Result<BinExpr>> {
-  return map(takeBin, split([';'], c));
+  const takeAltBinGroup: (s: ReadonlyArray<string>) => Result<BinExpr> =
+    (takeAlt<BinExpr>).bind(nothing(), takeBin, (takeGroup<BinExpr>).bind(nothing(), takeBin));
+
+  return map(takeAltBinGroup, split([';'], c));
 }