diff --git a/artiq/compiler/builtins.py b/artiq/compiler/builtins.py
index 8ca095b81..4b914063f 100644
--- a/artiq/compiler/builtins.py
+++ b/artiq/compiler/builtins.py
@@ -50,6 +50,10 @@ class TFloat(types.TMono):
     def one():
         return 1.0
 
+class TStr(types.TMono):
+    def __init__(self):
+        super().__init__("str")
+
 class TList(types.TMono):
     def __init__(self, elt=None):
         if elt is None:
@@ -88,6 +92,9 @@ def fn_int():
 def fn_float():
     return types.TConstructor("float")
 
+def fn_str():
+    return types.TConstructor("str")
+
 def fn_list():
     return types.TConstructor("list")
 
@@ -133,6 +140,9 @@ def get_int_width(typ):
 def is_float(typ):
     return types.is_mono(typ, "float")
 
+def is_str(typ):
+    return types.is_mono(typ, "str")
+
 def is_numeric(typ):
     typ = typ.find()
     return isinstance(typ, types.TMono) and \
@@ -167,6 +177,6 @@ def is_collection(typ):
     return isinstance(typ, types.TTuple) or \
         types.is_mono(typ, "list")
 
-def is_mutable(typ):
+def is_allocated(typ):
     return typ.fold(False, lambda accum, typ:
-        is_list(typ) or types.is_function(typ))
+        is_list(typ) or is_str(typ) or types.is_function(typ))
diff --git a/artiq/compiler/transforms/artiq_ir_generator.py b/artiq/compiler/transforms/artiq_ir_generator.py
index f449b4a2f..c18b987a2 100644
--- a/artiq/compiler/transforms/artiq_ir_generator.py
+++ b/artiq/compiler/transforms/artiq_ir_generator.py
@@ -565,6 +565,9 @@ class ARTIQIRGenerator(algorithm.Visitor):
     def visit_NumT(self, node):
         return ir.Constant(node.n, node.type)
 
+    def visit_StrT(self, node):
+        return ir.Constant(node.s, node.type)
+
     def visit_NameConstantT(self, node):
         return ir.Constant(node.value, node.type)
 
@@ -1038,7 +1041,7 @@ class ARTIQIRGenerator(algorithm.Visitor):
         return result
 
     def _compare_pair_identity(self, op, lhs, rhs):
-        if builtins.is_mutable(lhs) and builtins.is_mutable(rhs):
+        if builtins.is_allocated(lhs) and builtins.is_allocated(rhs):
             # These are actually pointers, compare directly.
             return self.append(ir.Compare(op, lhs, rhs))
         else:
diff --git a/artiq/compiler/transforms/asttyped_rewriter.py b/artiq/compiler/transforms/asttyped_rewriter.py
index 0c353bee6..df0b46d91 100644
--- a/artiq/compiler/transforms/asttyped_rewriter.py
+++ b/artiq/compiler/transforms/asttyped_rewriter.py
@@ -252,6 +252,11 @@ class ASTTypedRewriter(algorithm.Transformer):
         return asttyped.NumT(type=typ,
                              n=node.n, loc=node.loc)
 
+    def visit_Str(self, node):
+        return asttyped.StrT(type=builtins.TStr(),
+                             s=node.s,
+                             begin_loc=node.begin_loc, end_loc=node.end_loc, loc=node.loc)
+
     def visit_Name(self, node):
         return asttyped.NameT(type=self._find_name(node.id, node.loc),
                               id=node.id, ctx=node.ctx, loc=node.loc)
@@ -411,7 +416,6 @@ class ASTTypedRewriter(algorithm.Transformer):
     visit_GeneratorExp = visit_unsupported
     visit_Set = visit_unsupported
     visit_SetComp = visit_unsupported
-    visit_Str = visit_unsupported
     visit_Starred = visit_unsupported
     visit_Yield = visit_unsupported
     visit_YieldFrom = visit_unsupported
diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
index dcbcb3350..717c2f169 100644
--- a/artiq/compiler/transforms/llvm_ir_generator.py
+++ b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -18,7 +18,7 @@ class LLVMIRGenerator:
 
     def llty_of_type(self, typ, bare=False, for_return=False):
         if types.is_tuple(typ):
-            return ll.LiteralStructType([self.llty_of_type(eltty) for eltty in typ.elts])
+            return ll.LiteralStructType([self.llty_of_type(eltty) for eltty in typ.find().elts])
         elif types.is_function(typ):
             envarg = ll.IntType(8).as_pointer()
             llty = ll.FunctionType(args=[envarg] +
@@ -42,6 +42,8 @@ class LLVMIRGenerator:
             return ll.IntType(builtins.get_int_width(typ))
         elif builtins.is_float(typ):
             return ll.DoubleType()
+        elif builtins.is_str(typ):
+            return ll.IntType(8).as_pointer()
         elif builtins.is_list(typ):
             lleltty = self.llty_of_type(builtins.get_iterable_elt(typ))
             return ll.LiteralStructType([ll.IntType(32), lleltty.as_pointer()])
@@ -75,6 +77,14 @@ class LLVMIRGenerator:
             return ll.Constant(llty, False)
         elif isinstance(const.value, (int, float)):
             return ll.Constant(llty, const.value)
+        elif isinstance(const.value, str):
+            as_bytes = const.value.encode('utf-8')
+            llstrty = ll.ArrayType(ll.IntType(8), len(as_bytes))
+            llconst = ll.GlobalVariable(self.llmodule, llstrty,
+                                        name=self.llmodule.get_unique_name("str"))
+            llconst.global_constant = True
+            llconst.initializer = ll.Constant(llstrty, bytearray(as_bytes))
+            return llconst.bitcast(ll.IntType(8).as_pointer())
         else:
             assert False
 
@@ -157,7 +167,7 @@ class LLVMIRGenerator:
                                             size=llsize)
             llvalue = self.llbuilder.insert_value(llvalue, llalloc, 1, name=insn.name)
             return llvalue
-        elif builtins.is_mutable(insn.type):
+        elif builtins.is_allocated(insn.type):
             assert False
         else: # immutable
             llvalue = ll.Constant(self.llty_of_type(insn.type), ll.Undefined)
@@ -203,7 +213,7 @@ class LLVMIRGenerator:
         if types.is_tuple(insn.object().type):
             return self.llbuilder.extract_value(self.map(insn.object()), self.attr_index(insn),
                                                 name=insn.name)
-        elif not builtins.is_mutable(insn.object().type):
+        elif not builtins.is_allocated(insn.object().type):
             return self.llbuilder.extract_value(self.map(insn.object()), self.attr_index(insn),
                                                 name=insn.name)
         else:
@@ -213,7 +223,7 @@ class LLVMIRGenerator:
             return self.llbuilder.load(llptr)
 
     def process_SetAttr(self, insn):
-        assert builtins.is_mutable(insns.object().type)
+        assert builtins.is_allocated(insns.object().type)
         llptr = self.llbuilder.gep(self.map(insn.object()),
                                    [self.llindex(0), self.llindex(self.attr_index(insn))],
                                    name=insn.name)
diff --git a/artiq/compiler/validators/escape.py b/artiq/compiler/validators/escape.py
index fd030eeef..603b97d7d 100644
--- a/artiq/compiler/validators/escape.py
+++ b/artiq/compiler/validators/escape.py
@@ -78,7 +78,7 @@ class RegionOf(algorithm.Visitor):
     # Value lives as long as the current scope, if it's mutable,
     # or else forever
     def visit_BinOpT(self, node):
-        if builtins.is_mutable(node.type):
+        if builtins.is_allocated(node.type):
             return self.youngest_region
         else:
             return None
@@ -86,7 +86,7 @@ class RegionOf(algorithm.Visitor):
     # Value lives as long as the object/container, if it's mutable,
     # or else forever
     def visit_accessor(self, node):
-        if builtins.is_mutable(node.type):
+        if builtins.is_allocated(node.type):
             return self.visit(node.value)
         else:
             return None
@@ -125,20 +125,23 @@ class RegionOf(algorithm.Visitor):
     visit_ListCompT = visit_allocating
     visit_SetT = visit_allocating
     visit_SetCompT = visit_allocating
-    visit_StrT = visit_allocating
 
     # Value lives forever
     def visit_immutable(self, node):
-        assert not builtins.is_mutable(node.type)
+        assert not builtins.is_allocated(node.type)
         return None
 
-    visit_CompareT = visit_immutable
-    visit_EllipsisT = visit_immutable
     visit_NameConstantT = visit_immutable
     visit_NumT = visit_immutable
+    visit_EllipsisT = visit_immutable
     visit_UnaryOpT = visit_immutable
+    visit_CompareT = visit_immutable
     visit_CallT = visit_immutable
 
+    # Value is mutable, but still lives forever
+    def visit_StrT(self, node):
+        return None
+
     # Not implemented
     def visit_unimplemented(self, node):
         assert False
@@ -212,7 +215,7 @@ class EscapeValidator(algorithm.Visitor):
             self.youngest_env = {}
 
             for name in node.typing_env:
-                if builtins.is_mutable(node.typing_env[name]):
+                if builtins.is_allocated(node.typing_env[name]):
                     self.youngest_env[name] = Region(None) # not yet known
                 else:
                     self.youngest_env[name] = None # lives forever
@@ -277,7 +280,7 @@ class EscapeValidator(algorithm.Visitor):
             self.visit_assignment(target, node.value)
 
     def visit_AugAssign(self, node):
-        if builtins.is_mutable(node.target.type):
+        if builtins.is_allocated(node.target.type):
             # If the target is mutable, op-assignment will allocate
             # in the youngest region.
             self.visit_assignment(node.target, node.value, is_aug_assign=True)
@@ -295,7 +298,7 @@ class EscapeValidator(algorithm.Visitor):
             self.engine.process(diag)
 
     def visit_Raise(self, node):
-        if builtins.is_mutable(node.exc.type):
+        if builtins.is_allocated(node.exc.type):
             note = diagnostic.Diagnostic("note",
                 "this expression has type {type}",
                 {"type": types.TypePrinter().name(node.exc.type)},
diff --git a/lit-test/compiler/inferencer/unify.py b/lit-test/compiler/inferencer/unify.py
index 04c8aecbd..48681fdcb 100644
--- a/lit-test/compiler/inferencer/unify.py
+++ b/lit-test/compiler/inferencer/unify.py
@@ -54,3 +54,5 @@ not 1
 lambda x, y=1: x
 # CHECK-L: lambda x:'k, y:int(width='l)=1:int(width='l): x:'k:(x:'k, ?y:int(width='l))->'k
 
+k = "x"
+# CHECK-L: k:str