Merge pull request #1042 from quantified-uncertainty/getByWithFn

Changed getByWithFn to not need two function calls

packages/squiggle-lang/__tests__/E/A_test.res

@@ -0,0 +1,21 @@
+open Jest
+open TestHelpers
+
+describe("E.A.getByFmap", () => {
+  makeTest("Empty list returns None", E.A.getByFmap([], x => x + 1, x => mod(x, 2) == 0), None)
+  makeTest(
+    "Never predicate returns None",
+    E.A.getByFmap([1, 2, 3, 4, 5, 6], x => x + 1, _ => false),
+    None,
+  )
+  makeTest(
+    "function evaluates",
+    E.A.getByFmap([1, 1, 1, 1, 1, 1, 1, 2, 1, 1], x => 3 * x, x => x > 4),
+    Some(6),
+  )
+  makeTest(
+    "always predicate returns fn(fst(a))",
+    E.A.getByFmap([0, 1, 2, 3, 4, 5, 6], x => 10 + x, _ => true),
+    Some(10),
+  )
+})

packages/squiggle-lang/src/rescript/Utility/E.res

@@ -572,12 +572,22 @@ module A = {
       |> (x => Ok(x))
     }
 
-  let getByOpen = (a, op, bin) =>
+  let getByFmap = (a, fn, boolCondition) => {
-    switch getBy(a, r => bin(op(r))) {
+    let i = ref(0)
-    | Some(r) => Some(op(r))
+    let finalFunctionValue = ref(None)
-    | None => None
+    let length = Belt.Array.length(a)
+
+    while i.contents < length && finalFunctionValue.contents == None {
+      let itemWithFnApplied = Belt.Array.getUnsafe(a, i.contents) |> fn
+      if boolCondition(itemWithFnApplied) {
+        finalFunctionValue := Some(itemWithFnApplied)
+      }
+      i := i.contents + 1
     }
 
+    finalFunctionValue.contents
+  }
+
   let tail = Belt.Array.sliceToEnd(_, 1)
 
   let zip = Belt.Array.zip
@@ -680,7 +690,7 @@ module A = {
     let firstSome = x => Belt.Array.getBy(x, O.isSome)
 
     let firstSomeFn = (r: array<unit => option<'a>>): option<'a> =>
-      O.flatten(getByOpen(r, l => l(), O.isSome))
+      O.flatten(getByFmap(r, l => l(), O.isSome))
 
     let firstSomeFnWithDefault = (r, default) => firstSomeFn(r)->O2.default(default)