From 3d3dbff36263633034f6de97879890ba999cb2d6 Mon Sep 17 00:00:00 2001
From: Yann Hamdaoui <yann.hamdaoui@tweag.io>
Date: Fri, 16 Feb 2024 17:49:04 +0100
Subject: [PATCH] Update stdlib for ADTs

Update `std.enum` and various places of the stdlib to take into account
that now `std.typeof foo == 'Enum` might mean an enum tag or an enum
variant. Adds `std.enum.is_enum_tag` and `std.enum.is_enum_variant` to
the stdlib as well.
---
 core/stdlib/std.ncl   | 70 ++++++++++++++++++++++++++++++++++++-------
 doc/manual/merging.md |  7 ++---
 2 files changed, 63 insertions(+), 14 deletions(-)

diff --git a/core/stdlib/std.ncl b/core/stdlib/std.ncl
index 7c64e04823..36bf678aac 100644
--- a/core/stdlib/std.ncl
+++ b/core/stdlib/std.ncl
@@ -1549,7 +1549,7 @@
           error
         ```
       "%
-      = std.contract.from_predicate std.is_enum,
+      = std.contract.from_predicate is_enum_tag,
 
     TagOrString
       | doc m%%"
@@ -1557,8 +1557,8 @@
         converted to an enum tag.
 
         `TagOrString` is typically used in conjunction with an enum type, to
-        accept both actual enum tags and tags represented as strings (e.g. coming from a
-        JSON serialization).
+        accept both actual enum tags and tags represented as strings (e.g.
+        coming from a JSON serialization).
 
         **Warning**: contracts are applied in-order. The pattern described here
         requires that `TagOrString` is applied before the corresponding enum
@@ -1567,7 +1567,7 @@
 
         # Examples
 
-        ``` nickel
+        ```nickel
         let Schema = {
           protocol
             | std.enum.TagOrString
@@ -1589,15 +1589,63 @@
         ```
       "%%
       = fun label value =>
+        let label =
+          std.contract.label.with_message
+            "expected either a string or an enum tag"
+            label
+        in
         %typeof% value
         |> match {
           'String => %enum_from_str% value,
-          'Enum => value,
-          _ =>
-            std.contract.blame_with_message
-              "expected either a string or an enum tag"
-              label,
+          'Enum =>
+            if is_enum_variant value then
+              std.contract.blame label
+            else
+              value,
+          _ => std.contract.blame label,
         },
+
+    is_enum_tag
+      : Dyn -> Bool
+      | doc m%"
+        Checks if a value is an enum tag. Enum variants (applied to an argument)
+        aren't considered enum tags.
+
+        # Examples
+
+        ```nickel
+        std.enum.is_enum_tag 'foo
+          => true
+        std.enum.is_enum_tag 'FooBar
+          => true
+        std.enum.is_enum_tag "tag"
+          => false
+        std.enum.is_enum_tag ('Foo "arg")
+          => false
+        ```
+      "%
+      = fun value => std.is_enum value && !(%enum_is_variant% value),
+
+    is_enum_variant
+      : Dyn -> Bool
+      | doc m%"
+        Checks if a value is an enum variant. Bare enum tags (not applied to an
+        argument) aren't considered enum variants.
+
+        # Examples
+
+        ```nickel
+        std.enum.is_enum_variant ('Foo "arg")
+          => true
+        std.enum.is_enum_variant ('Http {version = "1.1"})
+          => true
+        std.enum.is_enum_variant 'foo
+          => false
+        std.enum.is_enum_variant [1, 2, 3]
+          => false
+        ```
+      "%
+      = fun value => %enum_is_variant% value,
   },
 
   function = {
@@ -2360,7 +2408,9 @@
               || type == 'Number
               || type == 'Bool
               || type == 'String
-              || type == 'Enum
+              # note that `type == 'Enum` isn't sufficient, as it includes enum
+              # variants
+              || std.enum.is_enum_tag value
           ),
 
     NonEmpty
diff --git a/doc/manual/merging.md b/doc/manual/merging.md
index 54014dd4c8..77298846fe 100644
--- a/doc/manual/merging.md
+++ b/doc/manual/merging.md
@@ -621,9 +621,9 @@ error: missing definition for `required_field2`
    8 │     & { foo.required_field1 = "here" }
      │             ------------------------ in this record
      │
-     ┌─ <stdlib/std.ncl>:3012:18
+     ┌─ <stdlib/std.ncl>:3062:18
      │
-3012 │     = fun x y => %deep_seq% x y,
+3062 │     = fun x y => %deep_seq% x y,
      │                  ------------ accessed here
 ```
 
@@ -640,8 +640,7 @@ let Port
       (
         fun value =>
           std.is_number value
-          && value
-          % 1 == 0
+          && value % 1 == 0
           && value >= 0
           && value <= 65535
       )