Add map_value_result + rename error (#346)

Author: Anton-4

examples/sqlite.roc

@@ -15,8 +15,8 @@ main! = |_args|
 
     List.for_each_try!(
         todo,
-        |{ id, task }|
-            Stdout.line!("\tid: ${id}, task: ${task}"),
+        |{ id, task, status }|
+            Stdout.line!("\tid: ${id}, task: ${task}, status: ${Inspect.to_str(status)}"),
     )?
 
     completed = query_todos_by_status!(db_path, "completed")?
@@ -25,8 +25,8 @@ main! = |_args|
 
     List.for_each_try!(
         completed,
-        |{ id, task }|
-            Stdout.line!("\tid: ${id}, task: ${task}"),
+        |{ id, task, status }|
+            Stdout.line!("\tid: ${id}, task: ${task}, status: ${Inspect.to_str(status)}"),
     )?
 
     Ok({})
@@ -35,12 +35,23 @@ query_todos_by_status! = |db_path, status|
     Sqlite.query_many!(
         {
             path: db_path,
-            query: "SELECT id, task FROM todos WHERE status = :status;",
+            query: "SELECT id, task, status FROM todos WHERE status = :status;",
             bindings: [{ name: ":status", value: String(status) }],
             # This uses the record builder syntax: https://www.roc-lang.org/examples/RecordBuilder/README.html
             rows: { Sqlite.decode_record <-
                 id: Sqlite.i64("id") |> Sqlite.map_value(Num.to_str),
                 task: Sqlite.str("task"),
+                status: Sqlite.str("status") |> Sqlite.map_value_result(decode_db_status),
             },
         },
     )
+
+TodoStatus : [Todo, Completed, InProgress]
+
+decode_db_status : Str -> Result TodoStatus _
+decode_db_status = |status_str|
+    when status_str is
+        "todo" -> Ok(Todo)
+        "completed" -> Ok(Completed)
+        "in-progress" -> Ok(InProgress)
+        _ -> Err(ParseError("Unknown status str: ${status_str}"))

examples/todos.db

@@ -43,6 +43,7 @@
           ]);
 
         sharedInputs = (with pkgs; [
+          sqlite
           jq
           rust
           llvmPkgs.clang

flake.lock

@@ -13,6 +13,7 @@ module [
     errcode_to_str,
     decode_record,
     map_value,
+    map_value_result,
     tagged_value,
     str,
     bytes,
@@ -336,7 +337,7 @@ query_many_prepared! = |{ stmt, bindings, rows: decode }|
     try(reset!, stmt)
     res
 
-SqlDecodeErr err : [FieldNotFound Str, SqliteErr ErrCode Str]err
+SqlDecodeErr err : [NoSuchField Str, SqliteErr ErrCode Str]err
 SqlDecode a err := List Str -> (Stmt => Result a (SqlDecodeErr err))
 
 ## Decode a Sqlite row into a record by combining decoders.
@@ -378,6 +379,31 @@ map_value = |@SqlDecode(gen_decode), mapper|
                 Ok(mapper(val)),
     )
 
+## Transform the output of a decoder by applying a function (that returns a Result) to the decoded value.
+## The Result is converted to SqlDecode.
+##
+## Example:
+## ```
+## decode_status : Str -> Result OnlineStatus UnknownStatusErr
+## decode_status = |status_str|
+##     when status_str is
+##         "online" -> Ok(Online)
+##         "offline" -> Ok(Offline)
+##         _ -> Err(UnknownStatus("${status_str}"))
+##
+## Sqlite.str("status") |> Sqlite.map_value_result(decode_status)
+## ```
+map_value_result : SqlDecode a err, (a -> Result c (SqlDecodeErr err)) -> SqlDecode c err
+map_value_result = |@SqlDecode(gen_decode), mapper|
+    @SqlDecode(
+        |cols|
+            decode! = gen_decode(cols)
+
+            |stmt|
+                val = try(decode!, stmt)
+                mapper(val),
+    )
+
 RowCountErr err : [NoRowsReturned, TooManyRowsReturned]err
 
 # internal use only
@@ -434,7 +460,7 @@ decoder = |fn|
 
                     Err(NotFound) ->
                         |_|
-                            Err(FieldNotFound(name)),
+                            Err(NoSuchField(name)),
         )
 
 ## Decode a [Value] keeping it tagged. This is useful when data could be many possible types.