refactor(validate): validate pred bakes identity, validateWith pred lens for custom lens

vic · vic · commit 3bb9da112261 · 2026-05-11T20:23:07.000-06:00
diff --git a/README.md b/README.md
@@ -40,7 +40,7 @@ Both `left` and `right` hold structured data, the library provides combinators f
 let lens = bend.pipe [
   (bend.attr "name")
   bend.str
-  (bend.validate (s: s != "") bend.identity)
+  (bend.validate (s: s != ""))
 ];
 in
 lens.get { name = "alice"; }   # right "alice"
@@ -230,7 +230,8 @@ in (bend.ensure validPort "invalid port" bend.int).get 80    # right 80
 | `focus getF setF`          | lift pure get/set into a lens              |
 | `parse fmap lens`          | apply fmap to focused value                |
 | `map f lens`               | transform focused value with pure function |
-| `validate pred lens`       | left when pred fails                       |
+| `validate pred`            | left when pred fails, focuses raw value    |
+| `validateWith pred lens`   | left when pred fails, with custom lens     |
 | `withDefault d lens`       | replace left with `right d`                |
 | `recover f lens`           | call f on left to attempt recovery         |
 | `alt lensA lensB`          | try lensA, fall back to lensB              |
diff --git a/default.nix b/default.nix
@@ -38,6 +38,7 @@ let
     inherit (parsers)
       map
       validate
+      validateWith
       int
       str
       bool
diff --git a/nix/parsers.nix b/nix/parsers.nix
@@ -2,9 +2,11 @@ either: adapt: parse: identity:
 let
   map = f: parse (a: either.right (f a));
 
-  validate = pred: parse (a: if pred a then either.right a else either.left a);
+  validateWith = pred: parse (a: if pred a then either.right a else either.left a);
 
-  typeParser = pred: parse (a: if pred a then either.right a else either.left a) identity;
+  validate = pred: validateWith pred identity;
+
+  typeParser = validate;
 
   int = typeParser builtins.isInt;
   str = typeParser builtins.isString;
@@ -34,6 +36,7 @@ in
   inherit
     map
     validate
+    validateWith
     int
     str
     bool
diff --git a/tests.nix b/tests.nix
@@ -312,12 +312,12 @@ in
     };
 
     validate."test-get-pred-pass-returns-right-same-value" = {
-      expr = (bend.validate (x: x > 0) bend.identity).get 5;
+      expr = (bend.validate (x: x > 0)).get 5;
       expected = bend.right 5;
     };
 
     validate."test-get-pred-fail-returns-left-same-value" = {
-      expr = (bend.validate (x: x > 0) bend.identity).get (-1);
+      expr = (bend.validate (x: x > 0)).get (-1);
       expected = bend.left (-1);
     };
 
@@ -484,7 +484,7 @@ in
           lens = bend.pipe [
             (bend.attr "name")
             bend.str
-            (bend.validate (s: s != "") bend.identity)
+            (bend.validate (s: s != ""))
           ];
         in
         lens.get { name = "alice"; };
@@ -497,7 +497,7 @@ in
           lens = bend.pipe [
             (bend.attr "name")
             bend.str
-            (bend.validate (s: s != "") bend.identity)
+            (bend.validate (s: s != ""))
           ];
         in
         lens.get { name = ""; };
@@ -640,7 +640,7 @@ in
     apply."test-apply-with-validation" = {
       expr =
         let
-          lens = bend.compose (bend.apply ({ x, y }: x + y)) (bend.validate (n: n > 20) bend.identity);
+          lens = bend.compose (bend.apply ({ x, y }: x + y)) (bend.validate (n: n > 20));
         in
         lens.get {
           x = 15;
@@ -652,7 +652,7 @@ in
     apply."test-apply-validation-fails" = {
       expr =
         let
-          lens = bend.compose (bend.apply ({ x, y }: x + y)) (bend.validate (n: n > 30) bend.identity);
+          lens = bend.compose (bend.apply ({ x, y }: x + y)) (bend.validate (n: n > 30));
         in
         lens.get {
           x = 15;
@@ -915,7 +915,7 @@ in
         let
           lens = bend.transform {
             x = bend.int;
-            y = bend.validate (s: builtins.stringLength s > 3) bend.str;
+            y = bend.validateWith (s: builtins.stringLength s > 3) bend.str;
           };
         in
         lens.get {
@@ -933,7 +933,7 @@ in
         let
           lens = bend.transform {
             x = bend.int;
-            y = bend.validate (s: builtins.stringLength s > 3) bend.str;
+            y = bend.validateWith (s: builtins.stringLength s > 3) bend.str;
           };
         in
         lens.get {
@@ -1541,11 +1541,11 @@ in
       expected = true;
     };
     predicate."test-andP-with-validate" = {
-      expr = (bend.validate (bend.andP (x: x > 0) (x: x < 100)) bend.identity).get 50;
+      expr = (bend.validate (bend.andP (x: x > 0) (x: x < 100))).get 50;
       expected = bend.right 50;
     };
     predicate."test-andP-with-validate-fails" = {
-      expr = (bend.validate (bend.andP (x: x > 0) (x: x < 100)) bend.identity).get 150;
+      expr = (bend.validate (bend.andP (x: x > 0) (x: x < 100))).get 150;
       expected = bend.left 150;
     };
     predicate."test-orP-with-ensure" = {
