feat(StateT): Add State eval functions

amsross · May 4, 2020 · fb2b65a · fb2b65a
1 parent 9377433
commit fb2b65a
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diff --git a/src/Transformers.re b/src/Transformers.re
@@ -59,6 +59,13 @@ module StateT = (T: Interface.TYPE, M: Interface.MONAD) => {
       let s' = f(s);
       M.pure((s', s'));
     };
+
+  let runWith: (T.t, t('a)) => m(('a, T.t)) =
+    (e, s) => s(e) |> M.map(((a, s)) => (s, a));
+  let evalWith: (T.t, t('a)) => m('a) =
+    (e, s) => runWith(e, s) |> M.map(fst);
+  let execWith: (T.t, t('a)) => m(T.t) =
+    (e, s) => runWith(e, s) |> M.map(snd);
 };
 
 module ReaderT = (T: Interface.TYPE, M: Interface.MONAD) => {

diff --git a/src/Transformers.rei b/src/Transformers.rei
@@ -26,6 +26,10 @@ module StateT:
     let get: t(T.t);
     let put: T.t => t(unit);
     let modify: (T.t => T.t) => t(T.t);
+
+    let runWith: (T.t, t('a)) => m(('a, T.t));
+    let evalWith: (T.t, t('a)) => m('a);
+    let execWith: (T.t, t('a)) => m(T.t);
   };
 
 module ReaderT: