From 97d79754dda571c28053c47f08d319b8a239021b Mon Sep 17 00:00:00 2001
From: Laria Carolin Chabowski <laria@laria.me>
Date: Mon, 31 Oct 2022 15:51:56 +0100
Subject: [PATCH] Implement while

---
 src/CMakeLists.txt            |  1 +
 src/apfl.h                    |  2 ++
 src/context.c                 |  7 +++++++
 src/functional-tests/while.at | 28 ++++++++++++++++++++++++++
 src/globals.c                 | 37 +++++++++++++++++++++++++++++++++++
 5 files changed, 75 insertions(+)
 create mode 100644 src/functional-tests/while.at

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 429017c..d748957 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -64,6 +64,7 @@ functionaltest("len")
 functionaltest("not")
 functionaltest("type")
 functionaltest("if")
+functionaltest("while")
 
 install(TARGETS apfl DESTINATION lib)
 install(TARGETS apfl-bin DESTINATION bin)
diff --git a/src/apfl.h b/src/apfl.h
index 71ed0cb..f2edde6 100644
--- a/src/apfl.h
+++ b/src/apfl.h
@@ -657,6 +657,8 @@ enum apfl_value_type apfl_get_type(apfl_ctx, apfl_stackidx);
 void apfl_drop(apfl_ctx, apfl_stackidx);
 // Move a value to the top of the stack
 void apfl_move_to_top_of_stack(apfl_ctx, apfl_stackidx);
+// Copy a value to the top of the stack
+void apfl_copy(apfl_ctx ctx, apfl_stackidx index);
 // Push a nil onto the stack
 void apfl_push_nil(apfl_ctx);
 // Push a boolean onto the stack
diff --git a/src/context.c b/src/context.c
index f3e30ea..ca1e98d 100644
--- a/src/context.c
+++ b/src/context.c
@@ -427,6 +427,13 @@ apfl_move_to_top_of_stack(apfl_ctx ctx, apfl_stackidx index)
     }
 }
 
+void
+apfl_copy(apfl_ctx ctx, apfl_stackidx index)
+{
+    struct apfl_value value = apfl_stack_must_get(ctx, index);
+    apfl_stack_must_push(ctx, apfl_value_set_cow_flag(value));
+}
+
 void
 apfl_stack_clear(apfl_ctx ctx)
 {
diff --git a/src/functional-tests/while.at b/src/functional-tests/while.at
new file mode 100644
index 0000000..9ba3faa
--- /dev/null
+++ b/src/functional-tests/while.at
@@ -0,0 +1,28 @@
+===== script =====
+i = 0
+while { (not (== i 10)) } {
+    print i
+    i = + i 1
+}
+
+i = 0
+print (while { (not (== i 10)) } {
+    i = + i 1
+    * 10 i
+})
+
+print (while {false} {"fail"})
+
+===== output =====
+0
+1
+2
+3
+4
+5
+6
+7
+8
+9
+100
+nil
diff --git a/src/globals.c b/src/globals.c
index c977162..2c501f4 100644
--- a/src/globals.c
+++ b/src/globals.c
@@ -274,6 +274,42 @@ type(apfl_ctx ctx)
     apfl_push_const_string(ctx, typestr(apfl_get_type(ctx, -1)));
 }
 
+static void
+impl_while(apfl_ctx ctx)
+{
+    size_t argc = apfl_len(ctx, 0);
+    if (argc != 2) {
+        apfl_raise_const_error(ctx, APFL_RESULT_ERR, "while needs 2 functions as arguments");
+    }
+
+    apfl_get_list_member_by_index(ctx, 0, 0);
+    if (apfl_get_type(ctx, -1) != APFL_VALUE_FUNC) {
+        apfl_raise_const_error(ctx, APFL_RESULT_ERR, "while needs 2 functions as arguments");
+    }
+    apfl_get_list_member_by_index(ctx, 0, 1);
+    if (apfl_get_type(ctx, -1) != APFL_VALUE_FUNC) {
+        apfl_raise_const_error(ctx, APFL_RESULT_ERR, "while needs 2 functions as arguments");
+    }
+
+    apfl_drop(ctx, 0);
+
+    apfl_push_nil(ctx); // Return value in case of no iteration
+
+    for (;;) {
+        apfl_copy(ctx, 0);
+        apfl_list_create(ctx, 0);
+        apfl_call(ctx, -2, -1);
+        if (!apfl_is_truthy(ctx, -1)) {
+            break;
+        }
+
+        apfl_drop(ctx, -1);
+        apfl_copy(ctx, 1);
+        apfl_list_create(ctx, 0);
+        apfl_call(ctx, -2, -1);
+    }
+}
+
 static const struct global_def globals[] = {
     {"if", impl_if},
     {"==", impl_eq},
@@ -288,6 +324,7 @@ static const struct global_def globals[] = {
     {"not", not},
     {"len", len},
     {"type", type},
+    {"while", impl_while},
     {NULL, NULL},
 };