add a typeof command (#597)

* add the `typeof` command

* add some tests

sourced/typeof.nu

@@ -0,0 +1,92 @@
+# give the type of the input data in a structured form
+def typeof [] {
+    let data = $in
+    let raw_type = $data | describe
+
+    match ($raw_type | str replace --regex "<.*" "") {
+        "list" => { {
+            type: "list"
+            items: ($raw_type | parse "list<{type}>" | get type.0)
+        } },
+        "record" => {
+            type: "record"
+            fields: ($data | columns | each {|field| {
+                name: $field,
+                type: ($data | get $field | typeof)
+            } } | transpose -rid)
+        },
+        "table" => {
+            type: "table"
+            columns: ($data | columns | each {|col| {
+                name: $col,
+                type: ($data | get $col | describe | parse "list<{type}>" | get type.0)
+            } } | transpose -rid)
+        },
+        _ => $raw_type
+    }
+}
+
+#[test]
+def simple_type [] {
+    use std assert
+
+    assert equal ("foo" | typeof) "string"
+    assert equal (123 | typeof) "int"
+    assert equal (true | typeof) "bool"
+}
+
+#[test]
+def list_type [] {
+    use std assert
+
+    assert equal ([1 2 3] | typeof) {type: "list", items: "int"}
+    assert equal (["foo" "bar" "baz"] | typeof) {type: "list", items: "string"}
+    assert equal (["foo" 2 true] | typeof) {type: "list", items: "any"}
+}
+
+#[test]
+def table_type [] {
+    use std assert
+    assert equal (ls | typeof) {
+        type: "table",
+        columns: {
+            name: "string",
+            type: "string",
+            size: "filesize",
+            modified: "date",
+        }
+    }
+}
+
+
+#[test]
+def record_type [] {
+    use std assert
+    assert equal ($nu | typeof) {
+        type: "record",
+        fields: {
+            default-config-dir: "string",
+            config-path: "string",
+            env-path: "string",
+            history-path: "string",
+            loginshell-path: "string",
+            plugin-path: "string",
+            home-path: "string",
+            temp-path: "string",
+            pid: "int",
+            os-info: {
+                type: "record",
+                fields: {
+                    name: "string",
+                    arch: "string",
+                    family: "string",
+                    kernel_version: "string",
+                }
+            },
+            startup-time: "duration",
+            is-interactive: "bool",
+            is-login: "bool",
+            current-exe: "string",
+        }
+    }
+}