feat: add support for negative steps in foreach

src/lua/zencode_foreach.lua

@@ -56,28 +56,50 @@ Foreach("'' in sequence from '' to '' with step ''", function(name, from_name, t
     if type(from) == 'zenroom.big' then
         -- only on first iteration: do checks and save usefull values
         if info.pos == 1 then
-            zencode_assert(BIG.zenpositive(step) and step ~= BIG.new(0), "only positive step is supported")
-            zencode_assert(BIG.zenpositive(BIG.zensub(to, from)), "end of foreach must be bigger than the start")
-            info.to_plus_1 = BIG.zenadd(to, BIG.new(1)) -- store to avoid repeating at each step
+            zencode_assert(step ~= BIG.new(0), "zero step is not supported")
+            local range_size = BIG.zensub(to, from)
+            if BIG.zenpositive(step) then
+                zencode_assert(BIG.zenpositive(range_size) or range_size == BIG.new(0), "end of foreach must be bigger than the start for postive step")
+                info.to_plus_1 = BIG.zenadd(to, BIG.new(1))
+                -- current_value >  to
+                -- current_value >= to + 1
+                -- (current_value - (to+1)) >= 0
+                info.check_fn = function ()
+                    local diff = BIG.zensub(info.cv, info.to_plus_1)
+                    return BIG.zenpositive(diff) or diff == BIG.new(0)
+                end
+            else
+                zencode_assert(not BIG.zenpositive(range_size) or range_size == BIG.new(0), "end of foreach must be smaller than the start for negative step")
+                info.to_minus_1 = BIG.zensub(to, BIG.new(1))
+                -- current_value < to
+                -- current_value <= to - 1
+                -- (current_value - (to-1)) <= 0
+                info.check_fn = function()
+                    local diff = BIG.zensub(info.cv, info.to_minus_1)
+                    return not BIG.zenpositive(diff) or diff == BIG.new(0)
+                end
+            end
             info.cv = from
         else
             info.cv = BIG.zenadd(info.cv, step)
         end
-        -- current_value >  to
-        -- current_value >= to + 1
-        -- (current_value - (to+1)) >= 0
-        local diff = BIG.zensub(info.cv, info.to_plus_1)
-        finished = BIG.zenpositive(diff) or diff == BIG.new(0)
+        finished = info.check_fn()
     else
         -- only on first iteration: do checks and save usefull values
         if info.pos == 1 then
-            zencode_assert(step > F.new(0) and from < to,
-                "only positive step is supported")
+            zencode_assert(step ~= F.new(0), "zero step is not supported")
+            if step > F.new(0) then
+                zencode_assert(from <= to, "end of foreach must be bigger than the start for postive step")
+                info.check_fn = function() return info.cv > to end
+            else
+                zencode_assert(from >= to, "end of foreach must be smaller than the start for negative step")
+                info.check_fn = function() return info.cv < to end
+            end
             info.cv = from
         else
             info.cv = info.cv + step
         end
-        finished = info.cv > to
+        finished = info.check_fn()
     end
 
     if finished then

test/zencode/foreach.bats

@@ -569,3 +569,66 @@ EOF
     run $ZENROOM_EXECUTABLE -c "maxiter=dec:10" -a maxiter.data.json -z maxiter_error_3.zen
     assert_line --partial 'Limit of iterations exceeded: 10'
 }
+
+@test "negative steps" {
+    cat << EOF | save_asset negative_steps.data.json
+{
+    "int_start": "1",
+    "int_end": "-10",
+    "int_step": "-1",
+    "num_start": 1,
+    "num_end": -10,
+    "num_step": -1
+}
+EOF
+    cat << EOF | zexe negative_steps.zen negative_steps.data.json
+Given I have a 'integer' named 'int_start'
+Given I have a 'integer' named 'int_end'
+Given I have a 'integer' named 'int_step'
+Given I have a 'number' named 'num_start'
+Given I have a 'number' named 'num_end'
+Given I have a 'number' named 'num_step'
+
+# integer loop with negative step
+When I create the 'integer array' named 'int_res'
+Foreach 'i' in sequence from 'int_start' to 'int_end' with step 'int_step'
+   When I move 'i' in 'int_res'
+EndForeach
+
+# integer loop with negative step that:
+# * start and end in the same negative number
+# * start and end in the same positive number
+When I create the 'integer array' named 'int_res_corner_case'
+Foreach 'i' in sequence from 'int_end' to 'int_end' with step 'int_step'
+   When I move 'i' in 'int_res_corner_case'
+EndForeach
+Foreach 'i' in sequence from 'int_start' to 'int_start' with step 'int_step'
+   When I move 'i' in 'int_res_corner_case'
+EndForeach
+
+# number loop with negative step
+When I create the 'integer array' named 'num_res'
+Foreach 'i' in sequence from 'num_start' to 'num_end' with step 'num_step'
+   When I move 'i' in 'num_res'
+EndForeach
+
+# number loop with negative step that:
+# * start and end in the same negative number
+# * start and end in the same positive number
+When I create the 'integer array' named 'num_res_corner_case'
+Foreach 'i' in sequence from 'num_end' to 'num_end' with step 'num_step'
+   When I move 'i' in 'num_res_corner_case'
+EndForeach
+Foreach 'i' in sequence from 'num_start' to 'num_start' with step 'num_step'
+   When I move 'i' in 'num_res_corner_case'
+EndForeach
+
+
+Then print the 'int_res'
+Then print the 'num_res'
+Then print the 'int_res_corner_case'
+Then print the 'num_res_corner_case'
+EOF
+    save_output negative_steps.out
+    assert_output '{"int_res":["1","0","-1","-2","-3","-4","-5","-6","-7","-8","-9","-10"],"int_res_corner_case":["-10","1"],"num_res":[1,0,-1,-2,-3,-4,-5,-6,-7,-8,-9,-10],"num_res_corner_case":[-10,1]}'
+}