From 91b2d3fcd73853e67100c5898b1a853adb7fe78b Mon Sep 17 00:00:00 2001
From: Lexy Plt <lexplt.dev@gmail.com>
Date: Thu, 12 Mar 2026 14:51:50 +0100
Subject: [PATCH 1/5] feat: ARK-344, pop! return the removed value, @= and @@=
 return the inserted value

---
 CHANGELOG.md                                  |  2 +
 docs/arkdoc/List.txt                          | 24 +++++++++++-
 docs/arkdoc/String.txt                        | 22 +++++++++++
 src/arkreactor/Compiler/BytecodeReader.cpp    |  4 ++
 .../Compiler/Lowerer/ASTLowerer.cpp           | 37 ++++++++++++++-----
 src/arkreactor/VM/VM.cpp                      | 23 ++++++++++++
 .../resources/LangSuite/list-tests.ark        | 14 ++++---
 .../resources/ParserSuite/success/compact.ark |  5 +++
 .../ParserSuite/success/compact.expected      |  5 +++
 9 files changed, 119 insertions(+), 17 deletions(-)
 create mode 100644 tests/unittests/resources/ParserSuite/success/compact.ark
 create mode 100644 tests/unittests/resources/ParserSuite/success/compact.expected

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 12ccef768..909283dfd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,8 @@
 - display a warning to `stderr` when using a deprecated function/value (checks for `@deprecated` inside the attached comment of functions / values)
 
 ### Changed
+- `pop!` can return the removed value
+- `@=` and `@@=` return the inserted value
 
 ### Removed
 
diff --git a/docs/arkdoc/List.txt b/docs/arkdoc/List.txt
index ef846fab8..fcdab9315 100644
--- a/docs/arkdoc/List.txt
+++ b/docs/arkdoc/List.txt
@@ -87,7 +87,7 @@
 
 --#
 * @name pop!
-* @brief Remove an element from a list in place, given its index. It doesn't return anything
+* @brief Remove an element from a list in place, given its index. Return the removed element
 * @details Supports negative indices, -1 being the end.
 * @param lst a list. Must be mutable
 * @param index number
@@ -157,3 +157,25 @@
 * (print (@@ ["abc" "def" "ghi"] 0 -1))  # c
 * =end
 #--
+
+--#
+* @name @=
+* @brief Set an element in a list, in place
+* @details Return the newly added element
+* @param lst list
+* @param index number (can be negative to start from the end)
+* @param x value
+* =begin
+* (mut lst [1 2 3 4 5])
+* (print (@= lst 0 "x"))  # "x"
+* (print lst)  # ["x" 2 3 4 5]
+* (print (@= lst 1 "y"))  # "y"
+* (print lst)  # ["x" "y" 3 4 5]
+* (print (@= lst 2 "z"))  # "z"
+* (print lst)  # ["x" "y" "z" 4 5]
+* (@= lst -1 "f")
+* (print lst)  # ["x" "y" "z" 4 "f"]
+* (@= lst -2 "g")
+* (print lst)  # ["x" "y" "z" "g" "f"]
+* =end
+#--
diff --git a/docs/arkdoc/String.txt b/docs/arkdoc/String.txt
index f0eea36a6..18e567179 100644
--- a/docs/arkdoc/String.txt
+++ b/docs/arkdoc/String.txt
@@ -77,3 +77,25 @@
 * (print (@ "abc" -2))  # "b"
 * =end
 #--
+
+--#
+* @name @=
+* @brief Set a character in a string, in place
+* @details Return the newly added character
+* @param str string
+* @param index number (can be negative to start from the end)
+* @param char character
+* =begin
+* (mut str "abcde")
+* (print (@= str 0 "x"))  # "x"
+* (print str)  # "xbcde"
+* (print (@= str 1 "y"))  # "y"
+* (print str)  # "xycde"
+* (print (@= str 2 "z"))  # "z"
+* (print str)  # "xyzde"
+* (@= str -1 "f")
+* (print str)  # "xyzdf"
+* (@= str -2 "g")
+* (print str)  # "xyzgf"
+* =end
+#--
diff --git a/src/arkreactor/Compiler/BytecodeReader.cpp b/src/arkreactor/Compiler/BytecodeReader.cpp
index b51f5be0a..ce1c294e0 100644
--- a/src/arkreactor/Compiler/BytecodeReader.cpp
+++ b/src/arkreactor/Compiler/BytecodeReader.cpp
@@ -513,6 +513,10 @@ namespace Ark
             { CONCAT, ArgKind::Raw },
             { APPEND_IN_PLACE, ArgKind::Raw },
             { CONCAT_IN_PLACE, ArgKind::Raw },
+            { POP_LIST, ArgKind::Raw },
+            { POP_LIST_IN_PLACE, ArgKind::Raw },
+            { SET_AT_INDEX, ArgKind::Raw },
+            { SET_AT_2_INDEX, ArgKind::Raw },
             { RESET_SCOPE_JUMP, ArgKind::Raw },
             { GET_CURRENT_PAGE_ADDR, ArgKind::Symbol },
             { LOAD_CONST_LOAD_CONST, ArgKind::ConstConst },
diff --git a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
index d595ed83a..7e0d6e60e 100644
--- a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
+++ b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
@@ -95,7 +95,7 @@ namespace Ark::internal
     bool ASTLowerer::nodeProducesOutput(const Node& node)
     {
         if (node.nodeType() == NodeType::List && !node.constList().empty() && node.constList()[0].nodeType() == NodeType::Keyword)
-            // a begin node produces a value if the last node in it produces a value
+            // a 'begin' node produces a value if the last node in it produces a value
             return (node.constList()[0].keyword() == Keyword::Begin && node.constList().size() > 1 && nodeProducesOutput(node.constList().back())) ||
                 // a function always produces a value ; even if it ends with a node not producing one, the VM returns nil
                 node.constList()[0].keyword() == Keyword::Fun ||
@@ -103,10 +103,14 @@ namespace Ark::internal
                 (node.constList()[0].keyword() == Keyword::If &&
                  nodeProducesOutput(node.constList()[2]) &&
                  (node.constList().size() == 3 || nodeProducesOutput(node.constList()[3])));
-        // in place list instruction, as well as breakpoint, do not produce values
+        // append! and concat! instructions, as well as breakpoint, do not produce values
         if (node.nodeType() == NodeType::List && !node.constList().empty() && node.constList()[0].nodeType() == NodeType::Symbol)
-            return std::ranges::find(Language::UpdateRef, node.constList().front().string()) == Language::UpdateRef.end() &&
-                node.constList().front().string() != "breakpoint";
+        {
+            const std::string& name = node.constList().front().string();
+            return name != Language::AppendInPlace &&
+                name != Language::ConcatInPlace &&
+                name != "breakpoint";
+        }
         return true;  // any other node, function call, symbol, number...
     }
 
@@ -332,15 +336,15 @@ namespace Ark::internal
     void ASTLowerer::compileListInstruction(Node& x, const Page p, const bool is_result_unused)
     {
         const Node head = x.constList()[0];
-        std::string name = x.constList()[0].string();
-        Instruction inst = getListInstruction(name).value();
+        const std::string& name = head.string();
+        const Instruction inst = getListInstruction(name).value();
 
         // length of at least 1 since we got a symbol name
         const auto argc = x.constList().size() - 1u;
         // error, can not use append/concat/pop (and their in place versions) with a <2 length argument list
-        if (argc < 2 && APPEND <= inst && inst <= POP)
+        if (argc < 2 && APPEND <= inst && inst <= SET_AT_2_INDEX)
             buildAndThrowError(fmt::format("Can not use {} with less than 2 arguments", name), head);
-        if (inst <= POP && std::cmp_greater(argc, MaxValue16Bits))
+        if (std::cmp_greater(argc, MaxValue16Bits))
             buildAndThrowError(fmt::format("Too many arguments ({}), exceeds {}", argc, MaxValue16Bits), x);
         if (argc != 3 && inst == SET_AT_INDEX)
             buildAndThrowError(fmt::format("Expected 3 arguments (list, index, value) for {}, got {}", name, argc), head);
@@ -366,24 +370,37 @@ namespace Ark::internal
                 break;
 
             case APPEND:
+                [[fallthrough]];
             case APPEND_IN_PLACE:
+                [[fallthrough]];
             case CONCAT:
+                [[fallthrough]];
             case CONCAT_IN_PLACE:
                 inst_argc = argc - 1;
                 break;
 
             case POP_LIST:
-            case POP_LIST_IN_PLACE:
                 inst_argc = 0;
                 break;
 
+            case SET_AT_INDEX:
+                [[fallthrough]];
+            case SET_AT_2_INDEX:
+                [[fallthrough]];
+            case POP_LIST_IN_PLACE:
+                inst_argc = is_result_unused ? 0 : 1;
+                break;
+
             default:
                 break;
         }
         page(p).emplace_back(inst, static_cast<uint16_t>(inst_argc));
         page(p).back().setSourceLocation(head.filename(), head.position().start.line);
 
-        if (is_result_unused && name.back() != '!' && inst <= POP_LIST_IN_PLACE)  // in-place functions never push a value
+        // append! and concat! do not push anything to the stack (for now)
+        // pop!, @= and @@= can push to the stack, but not using its returned value isn't an error
+        if (is_result_unused && inst != APPEND_IN_PLACE && inst != CONCAT_IN_PLACE &&
+            inst != POP_LIST_IN_PLACE && inst != SET_AT_INDEX && inst != SET_AT_2_INDEX)
         {
             warning("Ignoring return value of function", x);
             page(p).emplace_back(POP);
diff --git a/src/arkreactor/VM/VM.cpp b/src/arkreactor/VM/VM.cpp
index 6f6733811..71dee2df2 100644
--- a/src/arkreactor/VM/VM.cpp
+++ b/src/arkreactor/VM/VM.cpp
@@ -920,7 +920,14 @@ namespace Ark
                                     ErrorKind::Index,
                                     fmt::format("pop! index ({}) out of range (list size: {})", idx, list->list().size()));
 
+                            // Save the value we're removing to push it later.
+                            // We need to save the value and push later because we're using a pointer to 'list', and pushing before erasing
+                            // would overwrite values from the stack.
+                            if (arg)
+                                number = list->list()[static_cast<std::size_t>(idx)];
                             list->list().erase(list->list().begin() + idx);
+                            if (arg)
+                                push(number, context);
                         }
                         DISPATCH();
                     }
@@ -954,9 +961,17 @@ namespace Ark
                                     fmt::format("@= index ({}) out of range (indexable size: {})", idx, size));
 
                             if (list->valueType() == ValueType::List)
+                            {
                                 list->list()[static_cast<std::size_t>(idx)] = new_value;
+                                if (arg)
+                                    push(new_value, context);
+                            }
                             else
+                            {
                                 list->stringRef()[static_cast<std::size_t>(idx)] = new_value.string()[0];
+                                if (arg)
+                                    push(Value(new_value.string()[0]), context);
+                            }
                         }
                         DISPATCH();
                     }
@@ -1016,9 +1031,17 @@ namespace Ark
                                     fmt::format("@@= index (x: {}) out of range (inner indexable size: {})", idx_x, size));
 
                             if (is_list)
+                            {
                                 list->list()[static_cast<std::size_t>(idx_y)].list()[static_cast<std::size_t>(idx_x)] = new_value;
+                                if (arg)
+                                    push(new_value, context);
+                            }
                             else
+                            {
                                 list->list()[static_cast<std::size_t>(idx_y)].stringRef()[static_cast<std::size_t>(idx_x)] = new_value.string()[0];
+                                if (arg)
+                                    push(Value(new_value.string()[0]), context);
+                            }
                         }
                         DISPATCH();
                     }
diff --git a/tests/unittests/resources/LangSuite/list-tests.ark b/tests/unittests/resources/LangSuite/list-tests.ark
index a363d9a3c..25a9492c8 100644
--- a/tests/unittests/resources/LangSuite/list-tests.ark
+++ b/tests/unittests/resources/LangSuite/list-tests.ark
@@ -105,15 +105,15 @@
 
     (test:case "in place mutation with @=" {
         (mut numbers [0 1 2 3 4])
-        (@= numbers 2 5)
-        (@= numbers -1 9)
+        (test:eq (@= numbers 2 5) 5)
+        (test:eq (@= numbers -1 9) 9)
         (@= numbers -2 8)
         (test:eq numbers [0 1 5 8 9] "@=") })
 
     (test:case "in place 2D mutation with @@=" {
         (mut numbers [[0 1 2 3] [4 5 6 7] [8 9 0 1]])
-        (@@= numbers 0 0 9)
-        (@@= numbers 1 1 "a")
+        (test:eq (@@= numbers 0 0 9) 9)
+        (test:eq (@@= numbers 1 1 "a") "a")
         (@@= numbers -1 -1 -1)
         (@@= numbers -2 -2 -2)
         (test:eq numbers [[9 1 2 3] [4 "a" -2 7] [8 9 0 -1]]) })
@@ -126,9 +126,11 @@
         (concat! c d)
         (test:eq c [1 2 3 4 4 5 6])
         (test:eq d [4 5 6])
-        (pop! c -1)
+        (test:eq (pop! c -1) 6)
         (test:eq c [1 2 3 4 4 5])
-        (pop! c 1)
+        (test:eq (pop! c 1) 2)
         (test:eq c [1 3 4 4 5])
+        (pop! c 0)
+        (test:eq c [3 4 4 5])
         (test:eq a [1 2 3])
         (test:eq b [4 5 6]) })})
diff --git a/tests/unittests/resources/ParserSuite/success/compact.ark b/tests/unittests/resources/ParserSuite/success/compact.ark
new file mode 100644
index 000000000..2f0ecbf8e
--- /dev/null
+++ b/tests/unittests/resources/ParserSuite/success/compact.ark
@@ -0,0 +1,5 @@
+(+ 1a)
+(- 2b)
+(* 0c)
+(print 1"hello"d)
+(concat[1][2])
diff --git a/tests/unittests/resources/ParserSuite/success/compact.expected b/tests/unittests/resources/ParserSuite/success/compact.expected
new file mode 100644
index 000000000..9a5a7d23e
--- /dev/null
+++ b/tests/unittests/resources/ParserSuite/success/compact.expected
@@ -0,0 +1,5 @@
+( Symbol:+ Number:1 Symbol:a )
+( Symbol:- Number:2 Symbol:b )
+( Symbol:* Number:0 Symbol:c )
+( Symbol:print Number:1 String:hello Symbol:d )
+( Symbol:concat ( Symbol:list Number:1 ) ( Symbol:list Number:2 ) )

From bc94ca6bee398e44704548669227726a9c2e51c4 Mon Sep 17 00:00:00 2001
From: Lexy Plt <lexplt.dev@gmail.com>
Date: Thu, 12 Mar 2026 15:35:20 +0100
Subject: [PATCH 2/5] feat: ARK-344, append! and concat! return the modified
 list

---
 CHANGELOG.md                                  |  1 +
 docs/arkdoc/List.txt                          |  4 +--
 .../Compiler/Lowerer/ASTLowerer.cpp           | 19 +++++++-----
 .../CompilerSuite/optimized_ir/lists.ark      |  9 ++++++
 .../CompilerSuite/optimized_ir/lists.expected | 31 ++++++++++++++++---
 .../compileTime/apply_invalid_node.ark        |  2 +-
 .../compileTime/apply_invalid_node.expected   |  4 +--
 .../resources/LangSuite/list-tests.ark        |  4 +--
 8 files changed, 54 insertions(+), 20 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 909283dfd..c34a8409f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@
 ### Changed
 - `pop!` can return the removed value
 - `@=` and `@@=` return the inserted value
+- `append!` and `concat!` return the modified list
 
 ### Removed
 
diff --git a/docs/arkdoc/List.txt b/docs/arkdoc/List.txt
index fcdab9315..32c031ec7 100644
--- a/docs/arkdoc/List.txt
+++ b/docs/arkdoc/List.txt
@@ -35,7 +35,7 @@
 
 --#
 * @name append!
-* @brief Add an element to a list, modifying it in place. It doesn't return anything
+* @brief Add an element to a list, modifying it in place. Return the modified list
 * @param lst a list. Must be mutable
 * @param element
 * =begin
@@ -60,7 +60,7 @@
 
 --#
 * @name concat!
-* @brief Concatenate two lists in place, modifying the first one it in place. It doesn't return anything
+* @brief Concatenate two lists in place, modifying the first one it in place. Return the modified list
 * @param lst a list. Must be mutable
 * @param more another list
 * =begin
diff --git a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
index 7e0d6e60e..3ce2233d7 100644
--- a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
+++ b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
@@ -103,13 +103,11 @@ namespace Ark::internal
                 (node.constList()[0].keyword() == Keyword::If &&
                  nodeProducesOutput(node.constList()[2]) &&
                  (node.constList().size() == 3 || nodeProducesOutput(node.constList()[3])));
-        // append! and concat! instructions, as well as breakpoint, do not produce values
+        // breakpoint do not produce values
         if (node.nodeType() == NodeType::List && !node.constList().empty() && node.constList()[0].nodeType() == NodeType::Symbol)
         {
             const std::string& name = node.constList().front().string();
-            return name != Language::AppendInPlace &&
-                name != Language::ConcatInPlace &&
-                name != "breakpoint";
+            return name != "breakpoint";
         }
         return true;  // any other node, function call, symbol, number...
     }
@@ -397,10 +395,15 @@ namespace Ark::internal
         page(p).emplace_back(inst, static_cast<uint16_t>(inst_argc));
         page(p).back().setSourceLocation(head.filename(), head.position().start.line);
 
-        // append! and concat! do not push anything to the stack (for now)
-        // pop!, @= and @@= can push to the stack, but not using its returned value isn't an error
-        if (is_result_unused && inst != APPEND_IN_PLACE && inst != CONCAT_IN_PLACE &&
-            inst != POP_LIST_IN_PLACE && inst != SET_AT_INDEX && inst != SET_AT_2_INDEX)
+        if (!is_result_unused && (inst == APPEND_IN_PLACE || inst == CONCAT_IN_PLACE))
+        {
+            // Load the first argument which should be a symbol (or field),
+            // that append!/concat! write to, so that we have its new value available.
+            compileExpression(x.list()[1], p, false, false);
+        }
+
+        // append!, concat!, pop!, @= and @@= can push to the stack, but not using its returned value isn't an error
+        if (is_result_unused && (inst == LIST || inst == APPEND || inst == CONCAT || inst == POP_LIST))
         {
             warning("Ignoring return value of function", x);
             page(p).emplace_back(POP);
diff --git a/tests/unittests/resources/CompilerSuite/optimized_ir/lists.ark b/tests/unittests/resources/CompilerSuite/optimized_ir/lists.ark
index 6a5a0b4d4..ee8fb4e64 100644
--- a/tests/unittests/resources/CompilerSuite/optimized_ir/lists.ark
+++ b/tests/unittests/resources/CompilerSuite/optimized_ir/lists.ark
@@ -20,6 +20,15 @@
 
   # APPEND_IN_PLACE_SYM
   (append! source 6)
+  # APPEND_IN_PLACE_SYM
+  # + LOAD_FAST
+  (print (append! source 6))
+
+  # CONCAT_IN_PLACE
+  (concat! source [7])
+  # CONCAT_IN_PLACE
+  # + LOAD_FAST
+  (print (concat! source [7]))
 
   # AT_SYM_SYM
   (@ source n) }))
diff --git a/tests/unittests/resources/CompilerSuite/optimized_ir/lists.expected b/tests/unittests/resources/CompilerSuite/optimized_ir/lists.expected
index 7521508a7..520af99aa 100644
--- a/tests/unittests/resources/CompilerSuite/optimized_ir/lists.expected
+++ b/tests/unittests/resources/CompilerSuite/optimized_ir/lists.expected
@@ -5,16 +5,16 @@ page_0
 	STORE_LEN 0, 1
 	LOAD_CONST_STORE 3, 2
 	LOAD_CONST_STORE 4, 3
-	PUSH_RETURN_ADDRESS L0
+	PUSH_RETURN_ADDRESS L2
 	LOAD_FAST_BY_INDEX 0
 	CALL 0
-.L0:
+.L2:
 	POP 0
 	STORE_HEAD_BY_INDEX 3, 7
-	PUSH_RETURN_ADDRESS L1
+	PUSH_RETURN_ADDRESS L3
 	LOAD_FAST_BY_INDEX 0
 	CALL_BUILTIN 9, 1
-.L1:
+.L3:
 	POP 0
 	STORE_TAIL_BY_INDEX 4, 8
 	STORE_FROM_INDEX 5, 9
@@ -24,8 +24,9 @@ page_0
 	POP 0
 	AT_SYM_INDEX_CONST 6, 2
 	POP 0
-	LOAD_CONST 6
+	LOAD_CONST 7
 	APPEND_IN_PLACE_SYM_INDEX 1, 1
+	LOAD_FAST_BY_INDEX 1
 	HALT 0
 
 page_1
@@ -36,6 +37,26 @@ page_1
 	SET_VAL_TAIL 0, 6
 	LOAD_CONST 5
 	APPEND_IN_PLACE_SYM 0, 1
+	PUSH_RETURN_ADDRESS L0
+	LOAD_CONST 5
+	APPEND_IN_PLACE_SYM 0, 1
+	LOAD_FAST 0
+	CALL_BUILTIN 9, 1
+.L0:
+	POP 0
+	LOAD_CONST 6
+	LIST 1
+	LOAD_FAST 0
+	CONCAT_IN_PLACE 1
+	PUSH_RETURN_ADDRESS L1
+	LOAD_CONST 6
+	LIST 1
+	LOAD_FAST 0
+	CONCAT_IN_PLACE 1
+	LOAD_FAST 0
+	CALL_BUILTIN 9, 1
+.L1:
+	POP 0
 	AT_SYM_SYM 0, 2
 	RET 0
 	HALT 0
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.ark
index 182d88530..bed97acf5 100644
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.ark
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.ark
@@ -1,2 +1,2 @@
 (mut b [])
-(apply print (append! b 5))
+(apply print (breakpoint))
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.expected
index db280353d..796f8c00d 100644
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.expected
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.expected
@@ -1,6 +1,6 @@
 In file tests/unittests/resources/DiagnosticsSuite/compileTime/apply_invalid_node.ark:2
     1 | (mut b [])
-    2 | (apply print (append! b 5))
-      |              ^~~~~~~~~~~~~
+    2 | (apply print (breakpoint))
+      |              ^~~~~~~~~~~~
     3 |
         Invalid node inside call to `apply'. The given node doesn't return a value, and thus can't be used as an expression.
diff --git a/tests/unittests/resources/LangSuite/list-tests.ark b/tests/unittests/resources/LangSuite/list-tests.ark
index 25a9492c8..93f0f0871 100644
--- a/tests/unittests/resources/LangSuite/list-tests.ark
+++ b/tests/unittests/resources/LangSuite/list-tests.ark
@@ -121,9 +121,9 @@
     (test:case "in place list mutation" {
         (mut c a)
         (mut d b)
-        (append! c 4)
+        (test:eq (append! c 4) [1 2 3 4])
         (test:eq c [1 2 3 4])
-        (concat! c d)
+        (test:eq (concat! c d) [1 2 3 4 4 5 6])
         (test:eq c [1 2 3 4 4 5 6])
         (test:eq d [4 5 6])
         (test:eq (pop! c -1) 6)

From 115821b1bd22cd8ccbf12f50e8af3945036e20d6 Mon Sep 17 00:00:00 2001
From: Lexy Plt <lexplt.dev@gmail.com>
Date: Thu, 12 Mar 2026 17:44:14 +0100
Subject: [PATCH 3/5] feat: ARK-344, let, mut and set can return the assigned
 value

---
 CHANGELOG.md                                  |  1 +
 include/Ark/Compiler/Lowerer/ASTLowerer.hpp   |  2 +-
 .../Compiler/Lowerer/ASTLowerer.cpp           | 19 ++++--
 src/arkreactor/VM/Debugger.cpp                |  7 +-
 tests/unittests/Suites/DebuggerSuite.cpp      | 25 ++++----
 .../CompilerSuite/ir/closures.expected        |  1 +
 .../optimized_ir/builtins.expected            |  1 +
 .../optimized_ir/closures.expected            |  2 +
 .../CompilerSuite/optimized_ir/mul.expected   |  1 +
 .../resources/DebuggerSuite/basic.expected    | 14 ++--
 .../DebuggerSuite/debugger_quit.expected      |  8 +--
 .../resources/DebuggerSuite/loop.expected     | 16 ++---
 .../modify_program_state.expected             |  9 +--
 .../resources/DebuggerSuite/on_error.expected |  6 +-
 .../DebuggerSuite/stack_and_locals.expected   | 64 +++++++++----------
 .../compileTime/can_not_call_breakpoint.ark   |  1 +
 .../can_not_call_breakpoint.expected          |  5 ++
 .../compileTime/can_not_call_let.ark          |  1 -
 .../compileTime/can_not_call_let.expected     |  5 --
 .../compileTime/invalid_node_in_list.ark      |  2 +-
 .../compileTime/invalid_node_in_list.expected |  4 +-
 .../compileTime/or_1_breakpoint.ark           |  1 +
 .../compileTime/or_1_breakpoint.expected      |  5 ++
 .../DiagnosticsSuite/compileTime/or_1_mut.ark |  1 -
 .../compileTime/or_1_mut.expected             |  5 --
 .../DiagnosticsSuite/compileTime/or_let_1.ark |  1 -
 .../compileTime/or_let_1.expected             |  5 --
 .../resources/LangSuite/vm-tests.ark          | 13 ++++
 28 files changed, 125 insertions(+), 100 deletions(-)
 create mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.ark
 create mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.expected
 delete mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.ark
 delete mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.expected
 create mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.ark
 create mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.expected
 delete mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.ark
 delete mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.expected
 delete mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.ark
 delete mode 100644 tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.expected

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c34a8409f..6de96db49 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@
 - `pop!` can return the removed value
 - `@=` and `@@=` return the inserted value
 - `append!` and `concat!` return the modified list
+- `let`, `mut` and `set` can return the assigned value
 
 ### Removed
 
diff --git a/include/Ark/Compiler/Lowerer/ASTLowerer.hpp b/include/Ark/Compiler/Lowerer/ASTLowerer.hpp
index a4b5c5f88..820ed47e3 100644
--- a/include/Ark/Compiler/Lowerer/ASTLowerer.hpp
+++ b/include/Ark/Compiler/Lowerer/ASTLowerer.hpp
@@ -257,7 +257,7 @@ namespace Ark::internal
         void compileApplyInstruction(Node& x, Page p, bool is_result_unused);
         void compileIf(Node& x, Page p, bool is_result_unused, bool is_terminal);
         void compileFunction(Node& x, Page p, bool is_result_unused);
-        void compileLetMutSet(Keyword n, Node& x, Page p);
+        void compileLetMutSet(Keyword n, Node& x, Page p, bool is_result_unused);
         void compileWhile(Node& x, Page p);
         void compilePluginImport(const Node& x, Page p);
         void pushFunctionCallArguments(Node& call, Page p, bool is_tail_call);
diff --git a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
index 3ce2233d7..ce673cd49 100644
--- a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
+++ b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
@@ -99,6 +99,10 @@ namespace Ark::internal
             return (node.constList()[0].keyword() == Keyword::Begin && node.constList().size() > 1 && nodeProducesOutput(node.constList().back())) ||
                 // a function always produces a value ; even if it ends with a node not producing one, the VM returns nil
                 node.constList()[0].keyword() == Keyword::Fun ||
+                // a let/mut/set pushes the value that was assigned
+                node.constList()[0].keyword() == Keyword::Let ||
+                node.constList()[0].keyword() == Keyword::Mut ||
+                node.constList()[0].keyword() == Keyword::Set ||
                 // a condition produces a value if all its branches produce a value
                 (node.constList()[0].keyword() == Keyword::If &&
                  nodeProducesOutput(node.constList()[2]) &&
@@ -250,7 +254,7 @@ namespace Ark::internal
                     case Keyword::Let:
                         [[fallthrough]];
                     case Keyword::Mut:
-                        compileLetMutSet(keyword, x, p);
+                        compileLetMutSet(keyword, x, p, is_result_unused);
                         break;
 
                     case Keyword::Fun:
@@ -555,7 +559,7 @@ namespace Ark::internal
         }
     }
 
-    void ASTLowerer::compileLetMutSet(const Keyword n, Node& x, const Page p)
+    void ASTLowerer::compileLetMutSet(const Keyword n, Node& x, const Page p, const bool is_result_unused)
     {
         if (const auto sym = x.constList()[1]; sym.nodeType() != NodeType::Symbol)
             buildAndThrowError(fmt::format("Expected a symbol, got a {}", typeToString(sym)), sym);
@@ -577,17 +581,24 @@ namespace Ark::internal
 
         // put value before symbol id
         // starting at index = 2 because x is a (let|mut|set variable ...) node
-        for (std::size_t idx = 2, end = x.constList().size(); idx < end; ++idx)
-            compileExpression(x.list()[idx], p, false, false);
+        compileExpression(x.list()[2], p, false, false);
 
         if (n == Keyword::Let || n == Keyword::Mut)
         {
             page(p).emplace_back(STORE, i);
             m_locals_locator.addLocal(name);
+
+            if (!is_result_unused)
+                page(p).emplace_back(LOAD_FAST_BY_INDEX, 0);
         }
         else
+        {
             page(p).emplace_back(SET_VAL, i);
 
+            if (!is_result_unused)
+                page(p).emplace_back(LOAD_FAST, i);
+        }
+
         if (is_function)
             m_opened_vars.pop();
         page(p).back().setSourceLocation(x.filename(), x.position().start.line);
diff --git a/src/arkreactor/VM/Debugger.cpp b/src/arkreactor/VM/Debugger.cpp
index b3f561406..08ae3d9dc 100644
--- a/src/arkreactor/VM/Debugger.cpp
+++ b/src/arkreactor/VM/Debugger.cpp
@@ -179,7 +179,7 @@ namespace Ark::internal
         if (limit > 0 && count > 0)
         {
             fmt::println(m_os, "scope size: {}", limit);
-            fmt::println(m_os, "index |  id |    type   | value");
+            fmt::println(m_os, "index |  id |      name      |    type   | value");
             std::size_t i = 0;
 
             do
@@ -192,9 +192,10 @@ namespace Ark::internal
 
                 fmt::println(
                     m_os,
-                    "{:>5} | {:3} | {:>9} | {}",
+                    "{:>5} | {:3} | {:14} | {:>9} | {}",
                     fmt::styled(limit - i - 1, color),
                     fmt::styled(id, color),
+                    fmt::styled(vm.m_state.m_symbols[id], color),
                     fmt::styled(std::to_string(value.valueType()), color),
                     fmt::styled(value.toString(vm, /* show_as_code= */ true), color));
                 ++i;
@@ -257,7 +258,7 @@ namespace Ark::internal
                 m_os,
                 "dbg[{},{}]:{:0>3}{} ",
                 fmt::format("pp:{}", fmt::styled(pp, m_colorize ? fmt::fg(fmt::color::green) : fmt::text_style())),
-                fmt::format("ip:{}", fmt::styled(ip, m_colorize ? fmt::fg(fmt::color::cyan) : fmt::text_style())),
+                fmt::format("ip:{}", fmt::styled(ip / 4, m_colorize ? fmt::fg(fmt::color::cyan) : fmt::text_style())),
                 m_line_count,
                 unfinished_block ? ":" : ">");
 
diff --git a/tests/unittests/Suites/DebuggerSuite.cpp b/tests/unittests/Suites/DebuggerSuite.cpp
index 57a9369bf..4c72bfbf3 100644
--- a/tests/unittests/Suites/DebuggerSuite.cpp
+++ b/tests/unittests/Suites/DebuggerSuite.cpp
@@ -33,19 +33,18 @@ ut::suite<"Debugger"> debugger_suite = [] {
                 std::filesystem::path prompt_path(data.path);
                 prompt_path.replace_extension("prompt");
 
-                try
-                {
-                    Ark::VM vm(state);
-                    vm.usePromptFileForDebugger(prompt_path.generic_string(), os);
-                    vm.run(/* fail_with_exception= */ false);
-
-                    const std::string output = sanitizeOutput(os.str());
-                    expectOrDiff(data.expected, output);
-                }
-                catch (const std::exception&)
-                {
-                    expect(false);
-                }
+                expect(
+                    nothrow(
+                        [&] {
+                            Ark::VM vm(state);
+                            vm.usePromptFileForDebugger(prompt_path.generic_string(), os);
+                            vm.run(/* fail_with_exception= */ false);
+
+                            const std::string output = sanitizeOutput(os.str());
+                            expectOrDiff(data.expected, output);
+                            if (shouldWriteNewDiffsTofile() && data.expected != output)
+                                updateExpectedFile(data, output);
+                        }));
             };
         });
 };
diff --git a/tests/unittests/resources/CompilerSuite/ir/closures.expected b/tests/unittests/resources/CompilerSuite/ir/closures.expected
index 0bf9b580f..995722daf 100644
--- a/tests/unittests/resources/CompilerSuite/ir/closures.expected
+++ b/tests/unittests/resources/CompilerSuite/ir/closures.expected
@@ -111,6 +111,7 @@ page_2
 	STORE 5
 	LOAD_FAST_BY_INDEX 0
 	SET_VAL 2
+	LOAD_FAST 2
 	RET 0
 	HALT 0
 
diff --git a/tests/unittests/resources/CompilerSuite/optimized_ir/builtins.expected b/tests/unittests/resources/CompilerSuite/optimized_ir/builtins.expected
index a8c4a2277..fd6ed676d 100644
--- a/tests/unittests/resources/CompilerSuite/optimized_ir/builtins.expected
+++ b/tests/unittests/resources/CompilerSuite/optimized_ir/builtins.expected
@@ -2,6 +2,7 @@ page_0
 	LOAD_CONST_STORE 0, 0
 	LOAD_CONST_STORE 1, 2
 	LOAD_CONST_STORE 2, 4
+	LOAD_FAST_BY_INDEX 0
 	HALT 0
 
 page_1
diff --git a/tests/unittests/resources/CompilerSuite/optimized_ir/closures.expected b/tests/unittests/resources/CompilerSuite/optimized_ir/closures.expected
index 176d1d18d..bdae3566a 100644
--- a/tests/unittests/resources/CompilerSuite/optimized_ir/closures.expected
+++ b/tests/unittests/resources/CompilerSuite/optimized_ir/closures.expected
@@ -51,6 +51,7 @@ page_0
 .L7:
 	STORE 10
 	LOAD_CONST_STORE 18, 11
+	LOAD_FAST_BY_INDEX 0
 	HALT 0
 
 page_1
@@ -69,6 +70,7 @@ page_1
 page_2
 	STORE 5
 	SET_VAL_FROM_INDEX 0, 2
+	LOAD_FAST 2
 	RET 0
 	HALT 0
 
diff --git a/tests/unittests/resources/CompilerSuite/optimized_ir/mul.expected b/tests/unittests/resources/CompilerSuite/optimized_ir/mul.expected
index 4f7bcedc9..30431dfa1 100644
--- a/tests/unittests/resources/CompilerSuite/optimized_ir/mul.expected
+++ b/tests/unittests/resources/CompilerSuite/optimized_ir/mul.expected
@@ -18,5 +18,6 @@ page_1
 	STORE 2
 	MUL_SET_VAL 0, 2056
 	MUL_SET_VAL 0, 2056
+	LOAD_FAST 0
 	RET 0
 	HALT 0
diff --git a/tests/unittests/resources/DebuggerSuite/basic.expected b/tests/unittests/resources/DebuggerSuite/basic.expected
index 90fe228bc..5511b90c2 100644
--- a/tests/unittests/resources/DebuggerSuite/basic.expected
+++ b/tests/unittests/resources/DebuggerSuite/basic.expected
@@ -6,11 +6,11 @@ In file tests/unittests/resources/DebuggerSuite/basic.ark:3
     4 | (prn (format "ark: after first breakpoint, a={}, b={}" a b))
     5 |
 
-dbg[pp:0,ip:12]:000> (let c (+ a b))
-dbg[pp:0,ip:12]:001> (prn c)
+dbg[pp:0,ip:3]:000> (let c (+ a b))
 11
-nil
-dbg[pp:0,ip:12]:002> c
+dbg[pp:0,ip:3]:001> (prn c)
+11
+dbg[pp:0,ip:3]:002> c
 dbg: continue
 ark: after first breakpoint, a=5, b=6
 
@@ -23,17 +23,17 @@ In file tests/unittests/resources/DebuggerSuite/basic.ark:7
     8 |   (prn "ark: in (foo x y z), after second breakpoint")
     9 |   (+ x y z) }))
 
-dbg[pp:1,ip:20]:000> (prn x y z)
+dbg[pp:1,ip:5]:000> (prn x y z)
 567
 nil
-dbg[pp:1,ip:20]:001> help
+dbg[pp:1,ip:5]:001> help
 Available commands:
   help -- display this message
   c, continue -- resume execution
   q, quit -- quit the debugger, stopping the script execution
   stack <n=5> -- show the last n values on the stack
   locals <n=5> -- show the last n values on the locals' stack
-dbg[pp:1,ip:20]:001> continue
+dbg[pp:1,ip:5]:001> continue
 dbg: continue
 ark: in (foo x y z), after second breakpoint
 18
diff --git a/tests/unittests/resources/DebuggerSuite/debugger_quit.expected b/tests/unittests/resources/DebuggerSuite/debugger_quit.expected
index 0adb73182..a5df39493 100644
--- a/tests/unittests/resources/DebuggerSuite/debugger_quit.expected
+++ b/tests/unittests/resources/DebuggerSuite/debugger_quit.expected
@@ -6,9 +6,9 @@ In file tests/unittests/resources/DebuggerSuite/debugger_quit.ark:3
     4 | (prn (format "ark: after first breakpoint, a={}, b={}" a b))
     5 |
 
-dbg[pp:0,ip:12]:000> (let c (+ a b))
-dbg[pp:0,ip:12]:001> (prn c)
+dbg[pp:0,ip:3]:000> (let c (+ a b))
 11
-nil
-dbg[pp:0,ip:12]:002> q
+dbg[pp:0,ip:3]:001> (prn c)
+11
+dbg[pp:0,ip:3]:002> q
 dbg: stop
diff --git a/tests/unittests/resources/DebuggerSuite/loop.expected b/tests/unittests/resources/DebuggerSuite/loop.expected
index 424086953..0feebd27b 100644
--- a/tests/unittests/resources/DebuggerSuite/loop.expected
+++ b/tests/unittests/resources/DebuggerSuite/loop.expected
@@ -13,10 +13,10 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
     4 |   (prn (format "ark: i={}" i))
     5 |   (set i (+ 1 i)) })
 
-dbg[pp:0,ip:32]:000> (prn i)
+dbg[pp:0,ip:8]:000> (prn i)
 6
 nil
-dbg[pp:0,ip:32]:001> c
+dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=6
 
@@ -28,10 +28,10 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
     4 |   (prn (format "ark: i={}" i))
     5 |   (set i (+ 1 i)) })
 
-dbg[pp:0,ip:32]:000> (prn i)
+dbg[pp:0,ip:8]:000> (prn i)
 7
 nil
-dbg[pp:0,ip:32]:001> c
+dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=7
 
@@ -43,10 +43,10 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
     4 |   (prn (format "ark: i={}" i))
     5 |   (set i (+ 1 i)) })
 
-dbg[pp:0,ip:32]:000> (prn i)
+dbg[pp:0,ip:8]:000> (prn i)
 8
 nil
-dbg[pp:0,ip:32]:001> c
+dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=8
 
@@ -58,10 +58,10 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
     4 |   (prn (format "ark: i={}" i))
     5 |   (set i (+ 1 i)) })
 
-dbg[pp:0,ip:32]:000> (prn i)
+dbg[pp:0,ip:8]:000> (prn i)
 9
 nil
-dbg[pp:0,ip:32]:001> c
+dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=9
 ark: end
diff --git a/tests/unittests/resources/DebuggerSuite/modify_program_state.expected b/tests/unittests/resources/DebuggerSuite/modify_program_state.expected
index 75dc4b45d..682b7cf2f 100644
--- a/tests/unittests/resources/DebuggerSuite/modify_program_state.expected
+++ b/tests/unittests/resources/DebuggerSuite/modify_program_state.expected
@@ -13,10 +13,10 @@ In file tests/unittests/resources/DebuggerSuite/modify_program_state.ark:3
     4 |   (prn (format "ark: i={}" i))
     5 |   (set i (+ 1 i)) })
 
-dbg[pp:0,ip:32]:000> (prn i)
+dbg[pp:0,ip:8]:000> (prn i)
 6
 nil
-dbg[pp:0,ip:32]:001> c
+dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=6
 
@@ -28,8 +28,9 @@ In file tests/unittests/resources/DebuggerSuite/modify_program_state.ark:3
     4 |   (prn (format "ark: i={}" i))
     5 |   (set i (+ 1 i)) })
 
-dbg[pp:0,ip:32]:000> (set i 20)
-dbg[pp:0,ip:32]:001> c
+dbg[pp:0,ip:8]:000> (set i 20)
+20
+dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=20
 ark: end
diff --git a/tests/unittests/resources/DebuggerSuite/on_error.expected b/tests/unittests/resources/DebuggerSuite/on_error.expected
index e70e1a9c0..fd4e9435f 100644
--- a/tests/unittests/resources/DebuggerSuite/on_error.expected
+++ b/tests/unittests/resources/DebuggerSuite/on_error.expected
@@ -1,8 +1,8 @@
-dbg[pp:0,ip:12]:000> (prn a)
+dbg[pp:0,ip:3]:000> (prn a)
 5
 nil
-dbg[pp:0,ip:12]:001> (prn (type a))
+dbg[pp:0,ip:3]:001> (prn (type a))
 Number
 nil
-dbg[pp:0,ip:12]:002> c
+dbg[pp:0,ip:3]:002> c
 dbg: continue
diff --git a/tests/unittests/resources/DebuggerSuite/stack_and_locals.expected b/tests/unittests/resources/DebuggerSuite/stack_and_locals.expected
index f960fb2e3..4dc361ae9 100644
--- a/tests/unittests/resources/DebuggerSuite/stack_and_locals.expected
+++ b/tests/unittests/resources/DebuggerSuite/stack_and_locals.expected
@@ -7,16 +7,16 @@ In file tests/unittests/resources/DebuggerSuite/stack_and_locals.ark:8
     9 | (prn (f 1 2))
    10 |
 
-dbg[pp:0,ip:8]:000> stack
+dbg[pp:0,ip:2]:000> stack
 Stack is empty
 
-dbg[pp:0,ip:8]:000> locals
+dbg[pp:0,ip:2]:000> locals
 scope size: 2
-index |  id |    type   | value
-    1 |   0 |  Function | Function@1
-    0 |   4 |     CProc | CProcedure
+index |  id |      name      |    type   | value
+    1 |   0 | f              |  Function | Function@1
+    0 |   4 | prn            |     CProc | CProcedure
 
-dbg[pp:0,ip:8]:000> c
+dbg[pp:0,ip:2]:000> c
 dbg: continue
 
 In file tests/unittests/resources/DebuggerSuite/stack_and_locals.ark:3
@@ -27,38 +27,38 @@ In file tests/unittests/resources/DebuggerSuite/stack_and_locals.ark:3
     4 |   (if (= 1 a)
     5 |     (f "correct" "wrong")
 
-dbg[pp:1,ip:16]:000> stack
+dbg[pp:1,ip:4]:000> stack
 3 -> Instruction@28
 2 -> Function@0
 1 -> Instruction@32
 0 -> Function@0
 
-dbg[pp:1,ip:16]:000> locals 1
+dbg[pp:1,ip:4]:000> locals 1
 scope size: 3
-index |  id |    type   | value
-    2 |   3 |    Number | 1
+index |  id |      name      |    type   | value
+    2 |   3 | x              |    Number | 1
 
-dbg[pp:1,ip:16]:000> locals 2
+dbg[pp:1,ip:4]:000> locals 2
 scope size: 3
-index |  id |    type   | value
-    2 |   3 |    Number | 1
-    1 |   2 |    Number | 2
+index |  id |      name      |    type   | value
+    2 |   3 | x              |    Number | 1
+    1 |   2 | b              |    Number | 2
 
-dbg[pp:1,ip:16]:000> locals 3
+dbg[pp:1,ip:4]:000> locals 3
 scope size: 3
-index |  id |    type   | value
-    2 |   3 |    Number | 1
-    1 |   2 |    Number | 2
-    0 |   1 |    Number | 1
+index |  id |      name      |    type   | value
+    2 |   3 | x              |    Number | 1
+    1 |   2 | b              |    Number | 2
+    0 |   1 | a              |    Number | 1
 
-dbg[pp:1,ip:16]:000> locals
+dbg[pp:1,ip:4]:000> locals
 scope size: 3
-index |  id |    type   | value
-    2 |   3 |    Number | 1
-    1 |   2 |    Number | 2
-    0 |   1 |    Number | 1
+index |  id |      name      |    type   | value
+    2 |   3 | x              |    Number | 1
+    1 |   2 | b              |    Number | 2
+    0 |   1 | a              |    Number | 1
 
-dbg[pp:1,ip:16]:000> c
+dbg[pp:1,ip:4]:000> c
 dbg: continue
 
 In file tests/unittests/resources/DebuggerSuite/stack_and_locals.ark:3
@@ -69,19 +69,19 @@ In file tests/unittests/resources/DebuggerSuite/stack_and_locals.ark:3
     4 |   (if (= 1 a)
     5 |     (f "correct" "wrong")
 
-dbg[pp:1,ip:16]:000> stack
+dbg[pp:1,ip:4]:000> stack
 3 -> Instruction@28
 2 -> Function@0
 1 -> Instruction@32
 0 -> Function@0
 
-dbg[pp:1,ip:16]:000> locals
+dbg[pp:1,ip:4]:000> locals
 scope size: 3
-index |  id |    type   | value
-    2 |   3 |    String | "correct"
-    1 |   2 |    String | "wrong"
-    0 |   1 |    String | "correct"
+index |  id |      name      |    type   | value
+    2 |   3 | x              |    String | "correct"
+    1 |   2 | b              |    String | "wrong"
+    0 |   1 | a              |    String | "correct"
 
-dbg[pp:1,ip:16]:000> c
+dbg[pp:1,ip:4]:000> c
 dbg: continue
 correct
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.ark
new file mode 100644
index 000000000..a03603771
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.ark
@@ -0,0 +1 @@
+((breakpoint) builtin__list:slice [] 1 1 2)
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.expected
new file mode 100644
index 000000000..228dbfcab
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.expected
@@ -0,0 +1,5 @@
+In file tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_breakpoint.ark:1
+    1 | ((breakpoint) builtin__list:slice [] 1 1 2)
+      |  ^~~~~~~~~~~~
+    2 |
+        Can not call `(breakpoint)', as it doesn't return a value
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.ark
deleted file mode 100644
index 077cb83eb..000000000
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.ark
+++ /dev/null
@@ -1 +0,0 @@
-((let in (list 0 0 3 4 5)) builtin__list:slice in 1 1 2)
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.expected
deleted file mode 100644
index ab99a2a1b..000000000
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.expected
+++ /dev/null
@@ -1,5 +0,0 @@
-In file tests/unittests/resources/DiagnosticsSuite/compileTime/can_not_call_let.ark:1
-    1 | ((let in (list 0 0 3 4 5)) builtin__list:slice in 1 1 2)
-      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~
-    2 |
-        Can not call `(let in (list 0 0 3 4 5))', as it doesn't return a value
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.ark
index 4384732e5..6ca4b6854 100644
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.ark
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.ark
@@ -1 +1 @@
-[(mut c 1)]
+[(breakpoint)]
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.expected
index 6c22d23d3..4d4685075 100644
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.expected
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.expected
@@ -1,5 +1,5 @@
 In file tests/unittests/resources/DiagnosticsSuite/compileTime/invalid_node_in_list.ark:1
-    1 | [(mut c 1)]
-      |  ^~~~~~~~
+    1 | [(breakpoint)]
+      |  ^~~~~~~~~~~~
     2 |
         Invalid node inside call to `list'. The given node doesn't return a value, and thus can't be used as an expression.
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.ark
new file mode 100644
index 000000000..c2061b0df
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.ark
@@ -0,0 +1 @@
+(print (or 1 (breakpoint)))
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.expected
new file mode 100644
index 000000000..978b6ea4b
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.expected
@@ -0,0 +1,5 @@
+In file tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_breakpoint.ark:1
+    1 | (print (or 1 (breakpoint)))
+      |              ^~~~~~~~~~~~
+    2 |
+        Can not use `(breakpoint)' inside a `or' expression, as it doesn't return a value
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.ark
deleted file mode 100644
index 71ed4309f..000000000
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.ark
+++ /dev/null
@@ -1 +0,0 @@
-(print (or 1 (mut x 3)))
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.expected
deleted file mode 100644
index 7f7f68785..000000000
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.expected
+++ /dev/null
@@ -1,5 +0,0 @@
-In file tests/unittests/resources/DiagnosticsSuite/compileTime/or_1_mut.ark:1
-    1 | (print (or 1 (mut x 3)))
-      |              ^~~~~~~~
-    2 |
-        Can not use `(mut x 3)' inside a `or' expression, as it doesn't return a value
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.ark b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.ark
deleted file mode 100644
index e34b9f093..000000000
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.ark
+++ /dev/null
@@ -1 +0,0 @@
-(print (or (let x 1) 1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.expected b/tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.expected
deleted file mode 100644
index e2b2637e7..000000000
--- a/tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.expected
+++ /dev/null
@@ -1,5 +0,0 @@
-In file tests/unittests/resources/DiagnosticsSuite/compileTime/or_let_1.ark:1
-    1 | (print (or (let x 1) 1))
-      |            ^~~~~~~~
-    2 |
-        Can not use `(let x 1)' inside a `or' expression, as it doesn't return a value
diff --git a/tests/unittests/resources/LangSuite/vm-tests.ark b/tests/unittests/resources/LangSuite/vm-tests.ark
index 5a8cb2531..7430b578a 100644
--- a/tests/unittests/resources/LangSuite/vm-tests.ark
+++ b/tests/unittests/resources/LangSuite/vm-tests.ark
@@ -28,7 +28,20 @@
     (fun (&set-age &name &age) ()) }))
 (let bob (create-human "Bob" 38))
 
+(let egg (fun ((mut n))
+  (set n n)))
+
 (test:suite vm {
+    (test:case "assignments" {
+        (mut val (let x1 4))
+        (test:eq val 4)
+        (set val (mut x2 5))
+        (test:eq val 5)
+        (set val (set x2 6))
+        (test:eq val 6)
+        (set val (egg 7))
+        (test:eq val 7) })
+
     (test:case "arithmetic operations" {
         (test:eq (+ 1 2) 3)
         (test:eq (+ 1.5 2.5) 4.0)

From 1a1594ff4c47ae62236b73b13f600026b7fb37c4 Mon Sep 17 00:00:00 2001
From: Lexy Plt <lexplt.dev@gmail.com>
Date: Thu, 12 Mar 2026 18:31:20 +0100
Subject: [PATCH 4/5] chore: ARK-344, benchmarks comparison script color lines
 to make them easily identifiable

---
 tests/benchmarks/compare.py               | 16 +++++++++-------
 tests/benchmarks/results/013-74e64c67.csv | 11 +++++++++++
 2 files changed, 20 insertions(+), 7 deletions(-)
 create mode 100644 tests/benchmarks/results/013-74e64c67.csv

diff --git a/tests/benchmarks/compare.py b/tests/benchmarks/compare.py
index cda25992d..6ce013b37 100644
--- a/tests/benchmarks/compare.py
+++ b/tests/benchmarks/compare.py
@@ -127,24 +127,26 @@ def main(files: List[str]):
             runs_by_name[run.name].append(run)
 
     data = []
-    times = colorize_time_type("real_time", 0) + "\n" + colorize_time_type("cpu_time", 1)
 
-    for (name, runs) in runs_by_name.items():
+    for i, (name, runs) in enumerate(runs_by_name.items()):
         baseline: Run = runs[0]
         baseline_index = headers.index(baseline.benchmark) - 2
         diffs = [r.diff_from_baseline(baseline) for r in runs[1:]]
 
         padding = ["" for _ in range(baseline_index)] if baseline_index > 0 else []
         data.append(
-            [name, times] +
+            [
+                colorize_time_type(name, i % 2),
+                colorize_time_type("real_time", i % 2) + "\n" + colorize_time_type("cpu_time", i % 2)
+            ] +
             padding +
             [
-                colorize_time_type(f"{baseline.real_time:.3f}{baseline.time_unit}", 0) + "\n" +
-                colorize_time_type(f"{baseline.cpu_time:.3f}{baseline.time_unit}", 1)
+                colorize_time_type(f"{baseline.real_time:.3f}{baseline.time_unit}", i % 2) + "\n" +
+                colorize_time_type(f"{baseline.cpu_time:.3f}{baseline.time_unit}", i % 2)
             ] +
             [
-                f"{colorize_time_type(diff.dt_real_time, 0)} ({colorize_diff(diff.dt_rt_percent)}%)\n" +
-                f"{colorize_time_type(diff.dt_cpu_time, 1)} ({colorize_diff(diff.dt_ct_percent)}%)"
+                f"{colorize_time_type(diff.dt_real_time, i % 2)} ({colorize_diff(diff.dt_rt_percent)}%)\n" +
+                f"{colorize_time_type(diff.dt_cpu_time, i % 2)} ({colorize_diff(diff.dt_ct_percent)}%)"
                 for
                 diff in diffs
             ]
diff --git a/tests/benchmarks/results/013-74e64c67.csv b/tests/benchmarks/results/013-74e64c67.csv
new file mode 100644
index 000000000..2f178694c
--- /dev/null
+++ b/tests/benchmarks/results/013-74e64c67.csv
@@ -0,0 +1,11 @@
+name,iterations,real_time,cpu_time,time_unit,bytes_per_second,items_per_second,label,error_occurred,error_message
+"quicksort",7431,0.0933847,0.0930486,ms,,,,,
+"ackermann/iterations:50",50,32.3309,32.1861,ms,,,,,
+"fibonacci/iterations:100",100,3.16125,3.14818,ms,,,,,
+"builtins",1205,0.581715,0.580722,ms,,,,,
+"binary_trees",1,855.337,853.891,ms,,,,,
+"for_sum",8,88.2647,88.0911,ms,,,,,
+"create_closure/iterations:500",500,0.771819,0.770728,ms,,,,,
+"create_list/iterations:500",500,1.7033,1.70064,ms,,,,,
+"create_list_with_ref/iterations:500",500,1.46902,1.46652,ms,,,,,
+"n_queens/iterations:50",50,13.0718,13.0555,ms,,,,,

From 601ead9d84fa5c7c8406d533bae42f002f1c0c67 Mon Sep 17 00:00:00 2001
From: Lexy Plt <lexplt.dev@gmail.com>
Date: Thu, 12 Mar 2026 22:46:33 +0100
Subject: [PATCH 5/5] fix: when compiling code for the debugger, set
 is_result_unused to true

---
 src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp            | 8 +++++---
 tests/unittests/resources/DebuggerSuite/basic.expected    | 2 --
 .../resources/DebuggerSuite/debugger_quit.expected        | 1 -
 tests/unittests/resources/DebuggerSuite/loop.expected     | 4 ----
 .../resources/DebuggerSuite/modify_program_state.expected | 2 --
 tests/unittests/resources/DebuggerSuite/on_error.expected | 2 --
 6 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
index ce673cd49..0fbf9ec7e 100644
--- a/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
+++ b/src/arkreactor/Compiler/Lowerer/ASTLowerer.cpp
@@ -37,9 +37,11 @@ namespace Ark::internal
         // gather symbols, values, and start to create code segments
         compileExpression(
             ast,
-            /* current_page */ global,
-            /* is_result_unused */ false,
-            /* is_terminal */ false);
+            /* current_page= */ global,
+            // the offset is non-zero when coming from the debugger, and setting is_result_unused to
+            // true will avoid adding a LOAD_FAST/LOAD_FAST_FROM_INDEX after a let/mut/set
+            /* is_result_unused= */ m_start_page_at_offset != 0,
+            /* is_terminal= */ false);
         m_logger.traceEnd();
     }
 
diff --git a/tests/unittests/resources/DebuggerSuite/basic.expected b/tests/unittests/resources/DebuggerSuite/basic.expected
index 5511b90c2..cc189307c 100644
--- a/tests/unittests/resources/DebuggerSuite/basic.expected
+++ b/tests/unittests/resources/DebuggerSuite/basic.expected
@@ -7,7 +7,6 @@ In file tests/unittests/resources/DebuggerSuite/basic.ark:3
     5 |
 
 dbg[pp:0,ip:3]:000> (let c (+ a b))
-11
 dbg[pp:0,ip:3]:001> (prn c)
 11
 dbg[pp:0,ip:3]:002> c
@@ -25,7 +24,6 @@ In file tests/unittests/resources/DebuggerSuite/basic.ark:7
 
 dbg[pp:1,ip:5]:000> (prn x y z)
 567
-nil
 dbg[pp:1,ip:5]:001> help
 Available commands:
   help -- display this message
diff --git a/tests/unittests/resources/DebuggerSuite/debugger_quit.expected b/tests/unittests/resources/DebuggerSuite/debugger_quit.expected
index a5df39493..2b35cc5e3 100644
--- a/tests/unittests/resources/DebuggerSuite/debugger_quit.expected
+++ b/tests/unittests/resources/DebuggerSuite/debugger_quit.expected
@@ -7,7 +7,6 @@ In file tests/unittests/resources/DebuggerSuite/debugger_quit.ark:3
     5 |
 
 dbg[pp:0,ip:3]:000> (let c (+ a b))
-11
 dbg[pp:0,ip:3]:001> (prn c)
 11
 dbg[pp:0,ip:3]:002> q
diff --git a/tests/unittests/resources/DebuggerSuite/loop.expected b/tests/unittests/resources/DebuggerSuite/loop.expected
index 0feebd27b..b6bfc2f26 100644
--- a/tests/unittests/resources/DebuggerSuite/loop.expected
+++ b/tests/unittests/resources/DebuggerSuite/loop.expected
@@ -15,7 +15,6 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
 
 dbg[pp:0,ip:8]:000> (prn i)
 6
-nil
 dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=6
@@ -30,7 +29,6 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
 
 dbg[pp:0,ip:8]:000> (prn i)
 7
-nil
 dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=7
@@ -45,7 +43,6 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
 
 dbg[pp:0,ip:8]:000> (prn i)
 8
-nil
 dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=8
@@ -60,7 +57,6 @@ In file tests/unittests/resources/DebuggerSuite/loop.ark:3
 
 dbg[pp:0,ip:8]:000> (prn i)
 9
-nil
 dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=9
diff --git a/tests/unittests/resources/DebuggerSuite/modify_program_state.expected b/tests/unittests/resources/DebuggerSuite/modify_program_state.expected
index 682b7cf2f..2c83d8ce8 100644
--- a/tests/unittests/resources/DebuggerSuite/modify_program_state.expected
+++ b/tests/unittests/resources/DebuggerSuite/modify_program_state.expected
@@ -15,7 +15,6 @@ In file tests/unittests/resources/DebuggerSuite/modify_program_state.ark:3
 
 dbg[pp:0,ip:8]:000> (prn i)
 6
-nil
 dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=6
@@ -29,7 +28,6 @@ In file tests/unittests/resources/DebuggerSuite/modify_program_state.ark:3
     5 |   (set i (+ 1 i)) })
 
 dbg[pp:0,ip:8]:000> (set i 20)
-20
 dbg[pp:0,ip:8]:001> c
 dbg: continue
 ark: i=20
diff --git a/tests/unittests/resources/DebuggerSuite/on_error.expected b/tests/unittests/resources/DebuggerSuite/on_error.expected
index fd4e9435f..db0686aff 100644
--- a/tests/unittests/resources/DebuggerSuite/on_error.expected
+++ b/tests/unittests/resources/DebuggerSuite/on_error.expected
@@ -1,8 +1,6 @@
 dbg[pp:0,ip:3]:000> (prn a)
 5
-nil
 dbg[pp:0,ip:3]:001> (prn (type a))
 Number
-nil
 dbg[pp:0,ip:3]:002> c
 dbg: continue