Add stdlib function array.at_or

This is to return value at given position of array or default in case provided position is out of bound.
tweag · May 28, 2024 · 51ba172 · 51ba172
1 parent ca0f78f
commit 51ba172
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Showing 3 changed files with 27 additions and 8 deletions.
diff --git a/cli/tests/snapshot/snapshots/snapshot__eval_stderr_array_range_reversed_indices.ncl.snap b/cli/tests/snapshot/snapshots/snapshot__eval_stderr_array_range_reversed_indices.ncl.snap
@@ -4,9 +4,9 @@ expression: err
 ---
 error: contract broken by the caller of `range`
  invalid range
- ┌─ <stdlib/std.ncl>:649:9
+ ┌─ <stdlib/std.ncl>:672:9
  │
-649 │ | std.contract.unstable.RangeFun Dyn
+672 │ | std.contract.unstable.RangeFun Dyn
  │ ---------------------------------- expected type
  │
  ┌─ [INPUTS_PATH]/errors/array_range_reversed_indices.ncl:3:19
@@ -21,5 +21,3 @@ note:
  │
 3 │ std.array.range 1 0
  │ ------------------- (1) calling range
-
-
diff --git a/cli/tests/snapshot/snapshots/snapshot__eval_stderr_array_range_step_negative_step.ncl.snap b/cli/tests/snapshot/snapshots/snapshot__eval_stderr_array_range_step_negative_step.ncl.snap
@@ -4,9 +4,9 @@ expression: err
 ---
 error: contract broken by the caller of `range_step`
  invalid range step
- ┌─ <stdlib/std.ncl>:624:9
+ ┌─ <stdlib/std.ncl>:647:9
  │
-624 │ | std.contract.unstable.RangeFun (std.contract.unstable.RangeStep -> Dyn)
+647 │ | std.contract.unstable.RangeFun (std.contract.unstable.RangeStep -> Dyn)
  │ ----------------------------------------------------------------------- expected type
  │
  ┌─ [INPUTS_PATH]/errors/array_range_step_negative_step.ncl:3:27
@@ -26,5 +26,3 @@ note:
  │
 3 │ std.array.range_step 0 10 (-1)
  │ ------------------------------ (1) calling range_step
-
-
diff --git a/core/stdlib/std.ncl b/core/stdlib/std.ncl
@@ -172,6 +172,29 @@
  "%
  = fun n l => %elem_at% l n,
 
+ at_or
+ : forall a. Number -> a -> Array a -> a
+ | std.number.Nat -> Dyn
+ | doc m%"
+ Retrieves the n-th element from an array, with indices starting at 0
+ or provided value in case index is out of bounds.
+
+ # Examples
+
+ ```nickel
+ std.array.at_or 3 "default" [ "zero", "one", "two", "three" ] =>
+ "three"
+
+ std.array.at_or 3 "default" [ "zero", "one" ] =>
+ "default"
+ ```
+ "%
+ = fun n default_value array =>
+ if n < %length% array then
+ %elem_at% array n
+ else
+ default_value,
+
  concat
  : forall a. Array a -> Array a -> Array a
  | doc m%"