diff --git a/Cargo.lock b/Cargo.lock
index d1293939..d88e30b8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -62,7 +62,7 @@ dependencies = [
 
 [[package]]
 name = "bend-lang"
-version = "0.2.27"
+version = "0.2.28"
 dependencies = [
  "TSPL",
  "clap",
diff --git a/Cargo.toml b/Cargo.toml
index 79dfae58..a474068a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "bend-lang"
 description = "A high-level, massively parallel programming language"
 license = "Apache-2.0"
-version = "0.2.27"
+version = "0.2.28"
 edition = "2021"
 rust-version = "1.74"
 exclude = ["tests/snapshots/"]
diff --git a/docs/syntax.md b/docs/syntax.md
index 050213b9..7f469d83 100644
--- a/docs/syntax.md
+++ b/docs/syntax.md
@@ -142,6 +142,17 @@ The operations are:
 - Subtraction `-=`
 - Multiplication `*=`
 - Division `/=`
+- Bit And `&=`
+- Bit Or `|=`
+- Bit Xor `^=`
+- Mapper `@=`
+
+The mapper in-place operation applies a function and re-assigns the variable:
+
+```python
+x = "hello"
+x @= String/uppercase
+```
 
 ### Return
 
diff --git a/src/fun/builtins.bend b/src/fun/builtins.bend
index c7235f8b..f9ec3d4f 100644
--- a/src/fun/builtins.bend
+++ b/src/fun/builtins.bend
@@ -45,6 +45,19 @@ Map/set map key value =
       }
   }
 
+Map/map (Map/Leaf)                  key f = Map/Leaf
+Map/map (Map/Node value left right) key f =
+  switch _ = (== 0 key) {
+    0: switch _ = (% key 2) {
+      0:
+        (Map/Node value (Map/map left (/ key 2) f) right)
+      _:
+        (Map/Node value left (Map/map right (/ key 2) f))
+    }
+    _: (Map/Node (f value) left right)
+  }
+
+
 # IO Impl
 
 type IO:
diff --git a/src/imp/gen_map_get.rs b/src/imp/gen_map_get.rs
index 024c76b2..723f279f 100644
--- a/src/imp/gen_map_get.rs
+++ b/src/imp/gen_map_get.rs
@@ -39,12 +39,23 @@ impl Stmt {
           *self = gen_get(self, substitutions);
         }
       }
-      Stmt::InPlace { op: _, var: _, val, nxt } => {
+      Stmt::InPlace { op: _, pat, val, nxt } => {
+        let key_substitutions = if let AssignPattern::MapSet(_, key) = &mut **pat {
+          key.substitute_map_gets(id)
+        } else {
+          Vec::new()
+        };
+
         nxt.gen_map_get(id);
+
         let substitutions = val.substitute_map_gets(id);
         if !substitutions.is_empty() {
           *self = gen_get(self, substitutions);
         }
+
+        if !key_substitutions.is_empty() {
+          *self = gen_get(self, key_substitutions);
+        }
       }
       Stmt::If { cond, then, otherwise, nxt } => {
         then.gen_map_get(id);
diff --git a/src/imp/mod.rs b/src/imp/mod.rs
index 2198d045..b5537f37 100644
--- a/src/imp/mod.rs
+++ b/src/imp/mod.rs
@@ -72,6 +72,7 @@ pub enum InPlaceOp {
   And,
   Or,
   Xor,
+  Map,
 }
 
 #[derive(Clone, Debug, Default)]
@@ -85,7 +86,7 @@ pub enum Stmt {
   // {var} += {val} ";"? {nxt}
   InPlace {
     op: InPlaceOp,
-    var: Name,
+    pat: Box<AssignPattern>,
     val: Box<Expr>,
     nxt: Box<Stmt>,
   },
@@ -215,6 +216,7 @@ impl InPlaceOp {
       InPlaceOp::And => Op::AND,
       InPlaceOp::Or => Op::OR,
       InPlaceOp::Xor => Op::XOR,
+      InPlaceOp::Map => unreachable!(),
     }
   }
 }
diff --git a/src/imp/parser.rs b/src/imp/parser.rs
index 646a278c..196eef60 100644
--- a/src/imp/parser.rs
+++ b/src/imp/parser.rs
@@ -464,16 +464,20 @@ impl<'a> PyParser<'a> {
       return Ok((stmt, nxt_indent));
     }
     // In-place
-    if let AssignPattern::Var(name) = pat {
-      if let Some(op) = self.parse_in_place_op()? {
-        let val = self.parse_expr(true)?;
-        self.skip_trivia_inline();
-        self.try_consume_exactly(";");
-        self.consume_indent_exactly(*indent)?;
-        let (nxt, nxt_indent) = self.parse_statement(indent)?;
-        let stmt = Stmt::InPlace { op, var: name, val: Box::new(val), nxt: Box::new(nxt) };
-        return Ok((stmt, nxt_indent));
-      }
+
+    match &pat {
+      AssignPattern::Var(..) => {}
+      AssignPattern::MapSet(..) => {}
+      _ => self.expected_spanned("Var or Map accessor", ini_idx, end_idx)?,
+    }
+    if let Some(op) = self.parse_in_place_op()? {
+      let val = self.parse_expr(true)?;
+      self.skip_trivia_inline();
+      self.try_consume_exactly(";");
+      self.consume_indent_exactly(*indent)?;
+      let (nxt, nxt_indent) = self.parse_statement(indent)?;
+      let stmt = Stmt::InPlace { op, pat: Box::new(pat), val: Box::new(val), nxt: Box::new(nxt) };
+      return Ok((stmt, nxt_indent));
     }
 
     self.expected_spanned("statement", ini_idx, end_idx)
@@ -502,6 +506,9 @@ impl<'a> PyParser<'a> {
     } else if self.starts_with("^=") {
       self.consume("^=")?;
       Some(InPlaceOp::Xor)
+    } else if self.starts_with("@=") {
+      self.consume("@=")?;
+      Some(InPlaceOp::Map)
     } else {
       None
     };
diff --git a/src/imp/to_fun.rs b/src/imp/to_fun.rs
index 010af672..003d284a 100644
--- a/src/imp/to_fun.rs
+++ b/src/imp/to_fun.rs
@@ -1,4 +1,4 @@
-use super::{AssignPattern, Definition, Expr, Stmt};
+use super::{AssignPattern, Definition, Expr, InPlaceOp, Stmt};
 use crate::fun::{
   self,
   builtins::{LCONS, LNIL},
@@ -93,24 +93,78 @@ impl Stmt {
         let val = val.to_fun();
         StmtToFun::Assign(pat, val)
       }
-      Stmt::InPlace { op, var, val, nxt } => {
+      Stmt::InPlace { op, pat, val, nxt } => {
         let (nxt_pat, nxt) = match nxt.into_fun()? {
           StmtToFun::Return(term) => (None, term),
           StmtToFun::Assign(pat, term) => (Some(pat), term),
         };
-        let term = fun::Term::Let {
-          pat: Box::new(fun::Pattern::Var(Some(var.clone()))),
-          val: Box::new(fun::Term::Oper {
-            opr: op.to_lang_op(),
-            fst: Box::new(fun::Term::Var { nam: var }),
-            snd: Box::new(val.to_fun()),
-          }),
-          nxt: Box::new(nxt),
-        };
-        if let Some(pat) = nxt_pat {
-          StmtToFun::Assign(pat, term)
-        } else {
-          StmtToFun::Return(term)
+
+        // if it is a mapper operation
+        if let InPlaceOp::Map = op {
+          let term = match &*pat {
+            AssignPattern::MapSet(map, key) => {
+              let rhs = fun::Term::call(
+                fun::Term::r#ref("Map/map"),
+                [fun::Term::Var { nam: map.clone() }, key.clone().to_fun(), val.clone().to_fun()],
+              );
+              fun::Term::Let {
+                pat: Box::new(fun::Pattern::Var(Some(map.clone()))),
+                val: Box::new(rhs),
+                nxt: Box::new(nxt),
+              }
+            }
+            _ => {
+              let rhs = fun::Term::call(val.to_fun(), [pat.clone().into_fun().to_term()]);
+              fun::Term::Let { pat: Box::new(pat.into_fun()), val: Box::new(rhs), nxt: Box::new(nxt) }
+            }
+          };
+
+          if let Some(pat) = nxt_pat {
+            return Ok(StmtToFun::Assign(pat, term));
+          } else {
+            return Ok(StmtToFun::Return(term));
+          }
+        }
+
+        // otherwise
+        match *pat {
+          AssignPattern::Var(var) => {
+            let term = fun::Term::Let {
+              pat: Box::new(fun::Pattern::Var(Some(var.clone()))),
+              val: Box::new(fun::Term::Oper {
+                opr: op.to_lang_op(),
+                fst: Box::new(fun::Term::Var { nam: var }),
+                snd: Box::new(val.to_fun()),
+              }),
+              nxt: Box::new(nxt),
+            };
+            if let Some(pat) = nxt_pat {
+              StmtToFun::Assign(pat, term)
+            } else {
+              StmtToFun::Return(term)
+            }
+          }
+          AssignPattern::MapSet(map, key) => {
+            let temp = Name::new("%0");
+            let partial =
+              Expr::Opr { op: op.to_lang_op(), lhs: Box::new(Expr::Var { nam: temp.clone() }), rhs: val };
+            let map_fn = Expr::Lam { names: vec![(temp, false)], bod: Box::new(partial) };
+            let map_term = fun::Term::call(
+              fun::Term::r#ref("Map/map"),
+              [fun::Term::Var { nam: map.clone() }, key.to_fun(), map_fn.to_fun()],
+            );
+            let term = fun::Term::Let {
+              pat: Box::new(fun::Pattern::Var(Some(map))),
+              val: Box::new(map_term),
+              nxt: Box::new(nxt),
+            };
+            if let Some(pat) = nxt_pat {
+              StmtToFun::Assign(pat, term)
+            } else {
+              StmtToFun::Return(term)
+            }
+          }
+          _ => unreachable!(),
         }
       }
       Stmt::If { cond, then, otherwise, nxt } => {
diff --git a/tests/golden_tests/desugar_file/mapper_syntax.bend b/tests/golden_tests/desugar_file/mapper_syntax.bend
new file mode 100644
index 00000000..5e90bc67
--- /dev/null
+++ b/tests/golden_tests/desugar_file/mapper_syntax.bend
@@ -0,0 +1,7 @@
+def main:
+  x = 1
+  x @= lambda x: x + 1
+  map = { 0: 3, 1: 4 }
+  map[1] += 1
+  map[1] @= lambda x: x * 2
+  return (x, map[1], map[0])
diff --git a/tests/golden_tests/run_file/mapper_syntax.bend b/tests/golden_tests/run_file/mapper_syntax.bend
new file mode 100644
index 00000000..5e90bc67
--- /dev/null
+++ b/tests/golden_tests/run_file/mapper_syntax.bend
@@ -0,0 +1,7 @@
+def main:
+  x = 1
+  x @= lambda x: x + 1
+  map = { 0: 3, 1: 4 }
+  map[1] += 1
+  map[1] @= lambda x: x * 2
+  return (x, map[1], map[0])
diff --git a/tests/snapshots/desugar_file__mapper_syntax.bend.snap b/tests/snapshots/desugar_file__mapper_syntax.bend.snap
new file mode 100644
index 00000000..5d6ea8c2
--- /dev/null
+++ b/tests/snapshots/desugar_file__mapper_syntax.bend.snap
@@ -0,0 +1,85 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/desugar_file/mapper_syntax.bend
+---
+(Map/empty) = Map/Leaf
+
+(Map/get) = λa λb (a Map/get__C5 b)
+
+(Map/set) = λa λb λc (a Map/set__C10 c b)
+
+(Map/map) = λa λb λc (a Map/map__C5 b c)
+
+(main) = let (a, b) = main__C8; let (c, *) = (Map/get b 0); (main__C7, a, c)
+
+(Map/Node) = λa λb λc λd (d Map/Node/tag a b c)
+
+(Map/Leaf) = λa (a Map/Leaf/tag)
+
+(Map/Node/tag) = 0
+
+(Map/Leaf/tag) = 1
+
+(Map/get__C0) = λa λb λc λd let (e, f) = (Map/get c (/ a 2)); (e, (Map/Node b f d))
+
+(Map/get__C1) = λ* λa λb λc λd let (e, f) = (Map/get d (/ a 2)); (e, (Map/Node b c f))
+
+(Map/get__C2) = λa let {b c} = a; λd λe λf λ* (switch (% b 2) { 0: Map/get__C0; _: Map/get__C1; } c d e f)
+
+(Map/get__C3) = λ* λ* λa λ* λ* λb (a, b)
+
+(Map/get__C4) = λa let {b c} = a; λd let {e f} = d; λg let {h i} = g; λj let {k l} = j; (switch (== 0 k) { 0: Map/get__C2; _: Map/get__C3; } l b e h (Map/Node c f i))
+
+(Map/get__C5) = λa switch a { 0: Map/get__C4; _: λ* λ* (*, Map/Leaf); }
+
+(Map/map__C0) = λa λb λc λd λe (Map/Node e (Map/map d (/ b 2) a) c)
+
+(Map/map__C1) = λ* λa λb λc λd λe (Map/Node e d (Map/map c (/ b 2) a))
+
+(Map/map__C2) = λa λb let {c d} = b; λe λf λg (switch (% c 2) { 0: Map/map__C0; _: Map/map__C1; } a d e f g)
+
+(Map/map__C3) = λ* λa λ* λb λc λd (Map/Node (a d) c b)
+
+(Map/map__C4) = λa λb λc λd let {e f} = d; λg (switch (== 0 e) { 0: Map/map__C2; _: Map/map__C3; } g f c b a)
+
+(Map/map__C5) = λa switch a { 0: Map/map__C4; _: λ* λ* λ* Map/Leaf; }
+
+(Map/set__C0) = λa λb λc λd λe (Map/Node c (Map/set d (/ b 2) a) e)
+
+(Map/set__C1) = λ* λa λb λc λd λe (Map/Node c d (Map/set e (/ b 2) a))
+
+(Map/set__C10) = λa switch a { 0: Map/set__C8; _: Map/set__C9; }
+
+(Map/set__C2) = λa λb let {c d} = b; λe λf λg (switch (% c 2) { 0: Map/set__C0; _: Map/set__C1; } a d e f g)
+
+(Map/set__C3) = λ* λa λ* λ* λb λc (Map/Node a b c)
+
+(Map/set__C4) = λa λb (Map/Node * (Map/set Map/Leaf (/ b 2) a) Map/Leaf)
+
+(Map/set__C5) = λ* λa λb (Map/Node * Map/Leaf (Map/set Map/Leaf (/ b 2) a))
+
+(Map/set__C6) = λa λb let {c d} = b; (switch (% c 2) { 0: Map/set__C4; _: Map/set__C5; } a d)
+
+(Map/set__C7) = λ* λa λ* (Map/Node a Map/Leaf Map/Leaf)
+
+(Map/set__C8) = λa λb λc λd λe let {f g} = e; (switch (== 0 f) { 0: Map/set__C2; _: Map/set__C3; } d g a b c)
+
+(Map/set__C9) = λ* λa λb let {c d} = b; (switch (== 0 c) { 0: Map/set__C6; _: Map/set__C7; } a d)
+
+(main__C0) = (Map/set Map/empty 0 3)
+
+(main__C1) = λa (+ a 1)
+
+(main__C2) = (Map/set main__C0 1 4)
+
+(main__C3) = λa (* a 2)
+
+(main__C4) = (Map/map main__C2 1 main__C1)
+
+(main__C5) = (Map/map main__C4 1 main__C3)
+
+(main__C6) = λa (+ a 1)
+
+(main__C7) = (main__C6 1)
+
+(main__C8) = (Map/get main__C5 1)
diff --git a/tests/snapshots/run_file__mapper_syntax.bend.snap b/tests/snapshots/run_file__mapper_syntax.bend.snap
new file mode 100644
index 00000000..c1aa0101
--- /dev/null
+++ b/tests/snapshots/run_file__mapper_syntax.bend.snap
@@ -0,0 +1,9 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/run_file/mapper_syntax.bend
+---
+NumScott:
+((λa (+ a 1) 1), (10, 3))
+
+Scott:
+((λa (+ a 1) 1), (10, 3))