diff --git a/lib/js/src/Parser/Parser.bs.js b/lib/js/src/Parser/Parser.bs.js
index f82f778b..60d5edb8 100644
--- a/lib/js/src/Parser/Parser.bs.js
+++ b/lib/js/src/Parser/Parser.bs.js
@@ -1,21 +1,17 @@
 // Generated by ReScript, PLEASE EDIT WITH CARE
 'use strict';
 
-var Js_array = require("rescript/lib/js/js_array.js");
-var Js_string = require("rescript/lib/js/js_string.js");
 var Nodepath = require("node:path");
-var Belt_Array = require("rescript/lib/js/belt_Array.js");
-var Belt_Option = require("rescript/lib/js/belt_Option.js");
+var Core__Array = require("@rescript/core/lib/js/src/Core__Array.bs.js");
+var Core__Option = require("@rescript/core/lib/js/src/Core__Option.bs.js");
 
 function splitToLines(s) {
-  return Belt_Array.keepMap(Belt_Array.map((function (__x) {
-                      return Js_string.splitByRe(/\r\n|\n/, __x);
-                    })(s), (function (x) {
-                    if (x !== undefined && x !== "") {
-                      return x;
-                    }
-                    
-                  })), (function (x) {
+  return Core__Array.filterMap(s.split(/\r\n|\n/).map(function (x) {
+                  if (x !== undefined && x !== "") {
+                    return x;
+                  }
+                  
+                }), (function (x) {
                 return x;
               }));
 }
@@ -70,7 +66,7 @@ function make(initialContinuation, callback) {
 }
 
 function feed(self, input) {
-  var $$continue = Belt_Option.getWithDefault(self.continuation.contents, self.initialContinuation);
+  var $$continue = Core__Option.getOr(self.continuation.contents, self.initialContinuation);
   var err = $$continue(input);
   switch (err.TAG) {
     case "Error" :
@@ -133,15 +129,15 @@ function toString$1(x) {
   if (x.TAG === "A") {
     return "\"" + (x._0 + "\"");
   } else {
-    return "[" + (Js_array.joinWith(", ", Belt_Array.map(x._0, toString$1)) + "]");
+    return "[" + (x._0.map(toString$1).join(", ") + "]");
   }
 }
 
 function preprocess(string) {
-  if (Js_string.substring(0, 13, string) === "cannot read: ") {
+  if (string.substring(0, 13) === "cannot read: ") {
     return {
             TAG: "Error",
-            _0: Js_string.sliceToEnd(12, string),
+            _0: string.slice(12),
             [Symbol.for("name")]: "Error"
           };
   } else {
@@ -157,7 +153,7 @@ function flatten(x) {
   if (x.TAG === "A") {
     return [x._0];
   } else {
-    return Belt_Array.concatMany(Belt_Array.map(x._0, flatten));
+    return x._0.map(flatten).flat();
   }
 }
 
@@ -169,7 +165,7 @@ function parseWithContinuation(string) {
     var stack = state.stack;
     var pushToTheTop = function (elem) {
       var index = stack.length - 1 | 0;
-      var expr = Belt_Array.get(stack, index);
+      var expr = stack[index];
       if (expr === undefined) {
         return ;
       }
@@ -185,11 +181,11 @@ function parseWithContinuation(string) {
         };
         return ;
       }
-      Js_array.push(elem, xs._0);
+      xs._0.push(elem);
     };
     var totalLength = string.length;
     for(var i = 0; i < totalLength; ++i){
-      var $$char = Js_string.charAt(i, string);
+      var $$char = string.charAt(i);
       if (escaped.contents) {
         if ($$char === "n") {
           word.contents = word.contents + "\\";
@@ -198,13 +194,13 @@ function parseWithContinuation(string) {
         escaped.contents = false;
       } else if (!($$char === "\'" && !in_str.contents)) {
         if ($$char === "(" && !in_str.contents) {
-          Js_array.push({
+          stack.push({
                 contents: {
                   TAG: "L",
                   _0: [],
                   [Symbol.for("name")]: "L"
                 }
-              }, stack);
+              });
         } else if ($$char === ")" && !in_str.contents) {
           if (word.contents !== "") {
             pushToTheTop({
@@ -259,7 +255,7 @@ function parseWithContinuation(string) {
               [Symbol.for("name")]: "Continue"
             };
     }
-    var v = Belt_Array.get(stack, 0);
+    var v = stack[0];
     if (v === undefined) {
       return {
               TAG: "Error",
@@ -281,7 +277,7 @@ function parseWithContinuation(string) {
               [Symbol.for("name")]: "Error"
             };
     }
-    var w = Belt_Array.get(xs._0, 0);
+    var w = xs._0[0];
     if (w !== undefined) {
       return {
               TAG: "Done",
@@ -340,31 +336,31 @@ function parse(input) {
   var continuation = {
     contents: undefined
   };
-  Belt_Array.forEach(splitToLines(input), (function (line) {
-          var $$continue = Belt_Option.getWithDefault(continuation.contents, parseWithContinuation);
-          var err = $$continue(line);
-          switch (err.TAG) {
-            case "Error" :
-                Js_array.push({
-                      TAG: "Error",
-                      _0: err._0,
-                      [Symbol.for("name")]: "Error"
-                    }, resultAccum.contents);
-                return ;
-            case "Continue" :
-                continuation.contents = err._0;
-                return ;
-            case "Done" :
-                Js_array.push({
-                      TAG: "Ok",
-                      _0: err._0,
-                      [Symbol.for("name")]: "Ok"
-                    }, resultAccum.contents);
-                continuation.contents = undefined;
-                return ;
-            
-          }
-        }));
+  splitToLines(input).forEach(function (line) {
+        var $$continue = Core__Option.getOr(continuation.contents, parseWithContinuation);
+        var err = $$continue(line);
+        switch (err.TAG) {
+          case "Error" :
+              resultAccum.contents.push({
+                    TAG: "Error",
+                    _0: err._0,
+                    [Symbol.for("name")]: "Error"
+                  });
+              return ;
+          case "Continue" :
+              continuation.contents = err._0;
+              return ;
+          case "Done" :
+              resultAccum.contents.push({
+                    TAG: "Ok",
+                    _0: err._0,
+                    [Symbol.for("name")]: "Ok"
+                  });
+              continuation.contents = undefined;
+              return ;
+          
+        }
+      });
   return resultAccum.contents;
 }
 
@@ -394,13 +390,13 @@ var $$Error = {
 };
 
 function filepath(s) {
-  var removedBidi = Js_string.charCodeAt(0, s) === 8234.0 ? Js_string.sliceToEnd(1, s) : s;
+  var removedBidi = s.charCodeAt(0) === 8234.0 ? s.slice(1) : s;
   var normalized = Nodepath.normalize(removedBidi);
-  return Js_string.replaceByRe(/\\/g, "/", normalized);
+  return normalized.replace(/\\/g, "/");
 }
 
 function $$escape(s) {
-  return Js_string.replaceByRe(/\n/g, "\\n", Js_string.replaceByRe(/\r\n/g, "\\r\\n", Js_string.replaceByRe(/\"/g, "\\\"", Js_string.replaceByRe(/\\/g, "\\\\", s)))).trim();
+  return s.replace(/\\/g, "\\\\").replace(/\"/g, "\\\"").replace(/\r\n/g, "\\r\\n").replace(/\n/g, "\\n");
 }
 
 function unescapeEOL(s) {
diff --git a/lib/js/src/Parser/SourceFile.bs.js b/lib/js/src/Parser/SourceFile.bs.js
index efccbf45..ec37e23d 100644
--- a/lib/js/src/Parser/SourceFile.bs.js
+++ b/lib/js/src/Parser/SourceFile.bs.js
@@ -1,10 +1,9 @@
 // Generated by ReScript, PLEASE EDIT WITH CARE
 'use strict';
 
-var Js_string = require("rescript/lib/js/js_string.js");
-var Belt_Array = require("rescript/lib/js/belt_Array.js");
-var Belt_Option = require("rescript/lib/js/belt_Option.js");
 var Caml_option = require("rescript/lib/js/caml_option.js");
+var Core__Array = require("@rescript/core/lib/js/src/Core__Array.bs.js");
+var Core__Option = require("@rescript/core/lib/js/src/Core__Option.bs.js");
 var Parser$AgdaModeVscode = require("./Parser.bs.js");
 
 function parse(filepath) {
@@ -59,49 +58,47 @@ function lex(regex, source, target, tokens) {
     var cursor = {
       contents: token.range[0]
     };
-    return Belt_Array.map(Belt_Array.keepMap((function (__x) {
-                        return Js_string.splitByRe(regex, __x);
-                      })(token.content), (function (x) {
-                      return x;
-                    })), (function (content) {
-                  var kind = regex.test(content) ? target : source;
-                  var cursorOld = cursor.contents;
-                  cursor.contents = cursor.contents + content.length | 0;
-                  return {
-                          content: content,
-                          range: [
-                            cursorOld,
-                            cursor.contents
-                          ],
-                          kind: kind
-                        };
-                }));
+    return Core__Array.filterMap(token.content.split(regex), (function (x) {
+                    return x;
+                  })).map(function (content) {
+                var kind = regex.test(content) ? target : source;
+                var cursorOld = cursor.contents;
+                cursor.contents = cursor.contents + content.length | 0;
+                return {
+                        content: content,
+                        range: [
+                          cursorOld,
+                          cursor.contents
+                        ],
+                        kind: kind
+                      };
+              });
   };
-  return Belt_Array.concatMany(Belt_Array.map(tokens, f));
+  return tokens.map(f).flat();
 }
 
 function map(f, self) {
   var delta = {
     contents: 0
   };
-  return Belt_Array.map(self, (function (token) {
-                var match = f(token);
-                var content = match.content;
-                var match$1 = token.range;
-                var lengthDiff = content.length - token.content.length | 0;
-                var result_range = [
-                  match$1[0] + delta.contents | 0,
-                  (match$1[1] + delta.contents | 0) + lengthDiff | 0
-                ];
-                var result_kind = match.kind;
-                var result = {
-                  content: content,
-                  range: result_range,
-                  kind: result_kind
-                };
-                delta.contents = delta.contents + lengthDiff | 0;
-                return result;
-              }));
+  return self.map(function (token) {
+              var match = f(token);
+              var content = match.content;
+              var match$1 = token.range;
+              var lengthDiff = content.length - token.content.length | 0;
+              var result_range = [
+                match$1[0] + delta.contents | 0,
+                (match$1[1] + delta.contents | 0) + lengthDiff | 0
+              ];
+              var result_kind = match.kind;
+              var result = {
+                content: content,
+                range: result_range,
+                kind: result_kind
+              };
+              delta.contents = delta.contents + lengthDiff | 0;
+              return result;
+            });
 }
 
 function mapOnly(kind, f, self) {
@@ -164,27 +161,27 @@ function toTokens(raw) {
   var cursor = {
     contents: 0
   };
-  return Belt_Option.mapWithDefault(Js_string.match_(/(.*(?:\r\n|[\n\v\f\r\x85\u2028\u2029])?)/g, raw), [], (function (lines) {
-                return Belt_Array.map(Belt_Array.keep(Belt_Array.map(lines, (function (x) {
-                                      if (x !== undefined) {
-                                        return x;
-                                      } else {
-                                        return "";
-                                      }
-                                    })), (function (s) {
-                                  return s !== "";
-                                })), (function (line) {
-                              var cursorOld = cursor.contents;
-                              cursor.contents = cursor.contents + line.length | 0;
-                              return {
-                                      content: Js_string.substring(cursorOld, cursor.contents, raw),
-                                      range: [
-                                        cursorOld,
-                                        cursor.contents
-                                      ],
-                                      kind: "Literate"
-                                    };
-                            }));
+  return Core__Option.mapOr(Caml_option.nullable_to_opt(raw.match(/(.*(?:\r\n|[\n\v\f\r\x85\u2028\u2029])?)/g)), [], (function (lines) {
+                return lines.map(function (x) {
+                                if (x !== undefined) {
+                                  return x;
+                                } else {
+                                  return "";
+                                }
+                              }).filter(function (s) {
+                              return s !== "";
+                            }).map(function (line) {
+                            var cursorOld = cursor.contents;
+                            cursor.contents = cursor.contents + line.length | 0;
+                            return {
+                                    content: raw.substring(cursorOld, cursor.contents),
+                                    range: [
+                                      cursorOld,
+                                      cursor.contents
+                                    ],
+                                    kind: "Literate"
+                                  };
+                          });
               }));
 }
 
@@ -195,22 +192,22 @@ function markWithRules(begin_, end_, raw) {
   var current = {
     contents: false
   };
-  return Belt_Array.map(toTokens(raw), (function (token) {
-                var content = token.content;
-                previous.contents = current.contents;
-                if (begin_.test(content) && !current.contents) {
-                  current.contents = true;
-                } else if (end_.test(content) && current.contents) {
-                  current.contents = false;
-                }
-                var insideAgda = previous.contents && current.contents;
-                var kind = insideAgda ? "AgdaRaw" : "Literate";
-                return {
-                        content: content,
-                        range: token.range,
-                        kind: kind
-                      };
-              }));
+  return toTokens(raw).map(function (token) {
+              var content = token.content;
+              previous.contents = current.contents;
+              if (begin_.test(content) && !current.contents) {
+                current.contents = true;
+              } else if (end_.test(content) && current.contents) {
+                current.contents = false;
+              }
+              var insideAgda = previous.contents && current.contents;
+              var kind = insideAgda ? "AgdaRaw" : "Literate";
+              return {
+                      content: content,
+                      range: token.range,
+                      kind: kind
+                    };
+            });
 }
 
 function markMarkdown(extra) {
@@ -281,24 +278,16 @@ function parse$1(indices, filepath, raw) {
           };
   };
   var adjustGoalBracket = function (token) {
-    var idx = Belt_Array.get(indices, i.contents);
+    var idx = indices[i.contents];
     var goalIndex = idx !== undefined ? String(idx) : "*";
     var requiredSpaces = goalIndex.length;
-    var content = Belt_Option.getWithDefault(Belt_Option.flatMap(Caml_option.null_to_opt(goalBracketContent.exec(token.content)), (function (result) {
-                return Belt_Option.flatMap(Belt_Option.map(Belt_Array.get(result, 1), (function (prim) {
-                                  if (prim == null) {
-                                    return ;
-                                  } else {
-                                    return Caml_option.some(prim);
-                                  }
-                                })), (function (x) {
+    var content = Core__Option.getOr(Core__Option.flatMap(Caml_option.nullable_to_opt(goalBracketContent.exec(token.content)), (function (result) {
+                return Core__Option.flatMap(result[1], (function (x) {
                               return x;
                             }));
               })), "");
-    var actualSpaces = Belt_Option.getWithDefault(Belt_Option.flatMap((function (__x) {
-                  return Js_string.match_(/\s*$/, __x);
-                })(content), (function (matches) {
-                var match = Belt_Array.get(matches, 0);
+    var actualSpaces = Core__Option.getOr(Core__Option.flatMap(Caml_option.nullable_to_opt(content.match(/\s*$/)), (function (matches) {
+                var match = matches[0];
                 if (match === undefined) {
                   return ;
                 }
@@ -310,8 +299,8 @@ function parse$1(indices, filepath, raw) {
               })), 0);
     var newContent;
     if (actualSpaces < requiredSpaces) {
-      var padding = Js_string.repeat(requiredSpaces - actualSpaces | 0, "");
-      newContent = Js_string.replaceByRe(/\{!.*!\}/, "{!" + content + padding + "!}", token.content);
+      var padding = " ".repeat(requiredSpaces - actualSpaces | 0);
+      newContent = token.content.replace(/\{!.*!\}/, "{!" + content + padding + "!}");
     } else {
       newContent = token.content;
     }
@@ -326,30 +315,30 @@ function parse$1(indices, filepath, raw) {
           };
   };
   var modified = mapOnly("GoalBracket", adjustGoalBracket, mapOnly("GoalQM", questionMark2GoalBracket, original));
-  var originalHoles = Belt_Array.keep(original, isHole);
-  var modifiedHoles = Belt_Array.keep(modified, isHole);
-  return Belt_Array.keepMap(Belt_Array.mapWithIndex(originalHoles, (function (idx, token) {
-                    var match = Belt_Array.get(modifiedHoles, idx);
-                    var match$1 = Belt_Array.get(indices, idx);
-                    if (match === undefined) {
-                      return ;
-                    }
-                    if (match$1 === undefined) {
-                      return ;
-                    }
-                    var match$2 = match.range;
-                    var start = match$2[0];
-                    return {
-                            index: match$1,
-                            modifiedInterval: match.range,
-                            originalInterval: [
-                              start,
-                              start + token.content.length | 0
-                            ],
-                            content: match.content,
-                            changed: token.content !== match.content
-                          };
-                  })), (function (x) {
+  var originalHoles = original.filter(isHole);
+  var modifiedHoles = modified.filter(isHole);
+  return Core__Array.filterMap(originalHoles.map(function (token, idx) {
+                  var match = modifiedHoles[idx];
+                  var match$1 = indices[idx];
+                  if (match === undefined) {
+                    return ;
+                  }
+                  if (match$1 === undefined) {
+                    return ;
+                  }
+                  var match$2 = match.range;
+                  var start = match$2[0];
+                  return {
+                          index: match$1,
+                          modifiedInterval: match.range,
+                          originalInterval: [
+                            start,
+                            start + token.content.length | 0
+                          ],
+                          content: match.content,
+                          changed: token.content !== match.content
+                        };
+                }), (function (x) {
                 return x;
               }));
 }
diff --git a/src/Parser/Parser.res b/src/Parser/Parser.res
index 65b2d6a0..d1055eb9 100644
--- a/src/Parser/Parser.res
+++ b/src/Parser/Parser.res
@@ -1,9 +1,7 @@
-open Belt
-
 let splitToLines = s =>
   // RegEx updated to v10.1.4
   s
-  ->(Js.String.splitByRe(%re("/\r\n|\n/"), _))
+  ->String.splitByRegExp(%re("/\r\n|\n/"))
   ->Array.map(x =>
     switch x {
     | None => None
@@ -11,7 +9,7 @@ let splitToLines = s =>
     | Some(chunk) => Some(chunk)
     }
   )
-  ->Array.keepMap(x => x)
+  ->Array.filterMap(x => x)
 
 module Incr = {
   module Gen = {
@@ -57,7 +55,7 @@ module Incr = {
   // parsing with continuation
   let feed = (self: t<'a, 'e>, input: string): unit => {
     // get the existing continuation or initialize a new one
-    let continue = self.continuation.contents->Option.getWithDefault(self.initialContinuation)
+    let continue = self.continuation.contents->Option.getOr(self.initialContinuation)
 
     // continue parsing with the given continuation
     switch continue(input) {
@@ -96,7 +94,7 @@ module SExpression = {
   let rec toString = x =>
     switch x {
     | A(s) => "\"" ++ (s ++ "\"")
-    | L(xs) => "[" ++ (Js.Array.joinWith(", ", Array.map(xs, toString)) ++ "]")
+    | L(xs) => "[" ++ (xs->Array.map(toString)->Array.join(", ") ++ "]")
     }
 
   type state = {
@@ -107,8 +105,8 @@ module SExpression = {
   }
 
   let preprocess = (string: string): result<string, string> =>
-    if Js.String.substring(~from=0, ~to_=13, string) === "cannot read: " {
-      Error(Js.String.sliceToEnd(~from=12, string))
+    if String.substring(~start=0, ~end=13, string) === "cannot read: " {
+      Error(String.sliceToEnd(~start=12, string))
     } else {
       Ok(string)
     }
@@ -116,7 +114,7 @@ module SExpression = {
   let rec flatten: t => array<string> = x =>
     switch x {
     | A(s) => [s]
-    | L(xs) => xs->Array.map(flatten)->Array.concatMany
+    | L(xs) => xs->Array.map(flatten)->Array.flat
     }
 
   let parseWithContinuation = (string: string): Incr.continuation<
@@ -136,7 +134,7 @@ module SExpression = {
         | Some(expr) =>
           switch expr.contents {
           | A(_) => expr := L([expr.contents, elem])
-          | L(xs) => ignore(Js.Array.push(elem, xs))
+          | L(xs) => xs->Array.push(elem)
           }
         | None => ()
         }
@@ -145,7 +143,7 @@ module SExpression = {
       let totalLength = String.length(string)
 
       for i in 0 to totalLength - 1 {
-        let char = Js.String.charAt(i, string)
+        let char = string->String.charAt(i)
 
         if escaped.contents {
           /* something was being escaped */
@@ -158,13 +156,13 @@ module SExpression = {
         } else if char == "\'" && !in_str.contents {
           ()
         } else if char == "(" && !in_str.contents {
-          ignore(Js.Array.push(ref(L([])), stack))
+          stack->Array.push(ref(L([])))
         } else if char == ")" && !in_str.contents {
           if word.contents != "" {
             pushToTheTop(A(word.contents))
             word := ""
           }
-          switch Js.Array.pop(stack) {
+          switch Array.pop(stack) {
           | Some(expr) => pushToTheTop(expr.contents)
           | None => ()
           }
@@ -222,14 +220,14 @@ module SExpression = {
     ->splitToLines
     ->Array.forEach(line => {
       // get the parsing continuation or initialize a new one
-      let continue = continuation.contents->Option.getWithDefault(parseWithContinuation)
+      let continue = continuation.contents->Option.getOr(parseWithContinuation)
 
       // continue parsing with the given continuation
       switch continue(line) {
-      | Error(err) => ignore(Js.Array.push(Error(err), resultAccum.contents))
+      | Error(err) => resultAccum.contents->Array.push(Error(err))
       | Continue(continue) => continuation := Some(continue)
       | Done(result) =>
-        ignore(Js.Array.push(Ok(result), resultAccum.contents))
+        resultAccum.contents->Array.push(Ok(result))
         continuation := None
       }
     })
@@ -261,8 +259,8 @@ module Error = {
 
 let filepath = s => {
   // remove the Windows Bidi control character
-  let removedBidi = if Js.String.charCodeAt(0, s) === 8234.0 {
-    Js.String.sliceToEnd(~from=1, s)
+  let removedBidi = if String.charCodeAt(s, 0) === 8234.0 {
+    String.sliceToEnd(~start=1, s)
   } else {
     s
   }
@@ -271,7 +269,7 @@ let filepath = s => {
   let normalized = NodeJs.Path.normalize(removedBidi)
 
   // replace Windows' stupid backslash with slash
-  let replaced = Js.String.replaceByRe(%re("/\\/g"), "/", normalized)
+  let replaced = normalized->String.replaceRegExp(%re("/\\/g"), "/")
 
   replaced
 }
@@ -283,19 +281,12 @@ let filepath = s => {
 //      CR LF   => \r\n
 //      "       -> \"
 //      \       -> \\
-
 let escape = (s: string): string =>
-  Js.String.trim(
-    Js.String.replaceByRe(
-      %re("/\n/g"),
-      "\\n",
-      Js.String.replaceByRe(
-        %re("/\r\n/g"),
-        "\\r\\n",
-        Js.String.replaceByRe(%re("/\"/g"), "\\\"", Js.String.replaceByRe(%re("/\\/g"), "\\\\", s)),
-      ),
-    ),
-  )
+  s
+  ->String.replaceRegExp(%re("/\\/g"), "\\\\")
+  ->String.replaceRegExp(%re("/\"/g"), "\\\"")
+  ->String.replaceRegExp(%re("/\r\n/g"), "\\r\\n")
+  ->String.replaceRegExp(%re("/\n/g"), "\\n")
 
 // Almost the inverse of escape, but only for EOL characters.
 //
diff --git a/src/Parser/SourceFile.res b/src/Parser/SourceFile.res
index 17f5ea8f..1dc75bb0 100644
--- a/src/Parser/SourceFile.res
+++ b/src/Parser/SourceFile.res
@@ -1,6 +1,5 @@
 // All RegExps in this file has been updated to work with ReScript v10.1.4
 
-open Belt
 open Common
 
 module FileType = {
@@ -11,13 +10,13 @@ module FileType = {
     | LiterateMarkdown
     | LiterateOrg
   let parse = filepath =>
-    if Js.Re.test_(%re("/\.lagda\.rst$/i"), Parser.filepath(filepath)) {
+    if RegExp.test(%re("/\.lagda\.rst$/i"), Parser.filepath(filepath)) {
       LiterateRST
-    } else if Js.Re.test_(%re("/\.lagda\.md$/i"), Parser.filepath(filepath)) {
+    } else if RegExp.test(%re("/\.lagda\.md$/i"), Parser.filepath(filepath)) {
       LiterateMarkdown
-    } else if Js.Re.test_(%re("/\.lagda\.tex$|\.lagda$/i"), Parser.filepath(filepath)) {
+    } else if RegExp.test(%re("/\.lagda\.tex$|\.lagda$/i"), Parser.filepath(filepath)) {
       LiterateTeX
-    } else if Js.Re.test_(%re("/\.lagda\.org$/i"), Parser.filepath(filepath)) {
+    } else if RegExp.test(%re("/\.lagda\.org$/i"), Parser.filepath(filepath)) {
       LiterateOrg
     } else {
       Agda
@@ -57,15 +56,15 @@ module Lexer = {
      regex     : regex to perform split on a token
      sourceType: the type of token to look for and perform splitting
      targetType: the type of token given to the splitted tokens when identified */
-  let lex = (regex: Js.Re.t, source: Token.kind, target: Token.kind, tokens): t => {
+  let lex = (regex: RegExp.t, source: Token.kind, target: Token.kind, tokens): t => {
     let f = (token: Token.t) =>
       if token.kind === source {
         let cursor = ref(fst(token.range))
         token.content
-        ->Js.String.splitByRe(regex, _)
-        ->Array.keepMap(x => x)
+        ->String.splitByRegExp(regex)
+        ->Array.filterMap(x => x)
         ->Array.map(content => {
-          let kind = Js.Re.test_(regex, content) ? target : source
+          let kind = RegExp.test(regex, content) ? target : source
           let cursorOld = cursor.contents
           cursor := cursor.contents + String.length(content)
           open Token
@@ -74,7 +73,7 @@ module Lexer = {
       } else {
         [token]
       }
-    tokens->Array.map(f)->Array.concatMany
+    tokens->Array.map(f)->Array.flat
   }
 
   // transforms a list of tokens while preserving the ranges
@@ -99,7 +98,7 @@ module Lexer = {
 
   // only apply map(f) on a specific tokenType
   let mapOnly = (kind: Token.kind, f: Token.t => Token.t, self): t =>
-    self |> map(token => token.kind === kind ? f(token) : token)
+    map(token => token.kind === kind ? f(token) : token, self)
 }
 
 module Regex = {
@@ -134,10 +133,9 @@ module Literate = {
   // split a single string into tokens (Literate)
   let toTokens = (raw: string): Lexer.t => {
     let cursor = ref(0)
-    Js.String.match_(
-      %re("/(.*(?:\r\n|[\n\v\f\r\x85\u2028\u2029])?)/g"),
-      raw,
-    )->Option.mapWithDefault([], lines =>
+    raw
+    ->String.match(%re("/(.*(?:\r\n|[\n\v\f\r\x85\u2028\u2029])?)/g"))
+    ->Option.mapOr([], lines =>
       lines
       ->Array.map(x =>
         switch x {
@@ -145,14 +143,14 @@ module Literate = {
         | Some(s) => s
         }
       )
-      ->Array.keep(s => s != "")
+      ->Array.filter(s => s != "")
       ->Array.map(line => {
         // [\s\.\;\{\}\(\)\@]
         let cursorOld = cursor.contents
         cursor := cursor.contents + String.length(line)
         open Token
         {
-          content: Js.String.substring(~from=cursorOld, ~to_=cursor.contents, raw),
+          content: String.substring(~start=cursorOld, ~end=cursor.contents, raw),
           range: (cursorOld, cursor.contents),
           kind: Literate,
         }
@@ -173,10 +171,10 @@ module Literate = {
       // update the previous line
       previous := current.contents
 
-      if Js.Re.test_(begin_, content) && !current.contents {
+      if RegExp.test(begin_, content) && !current.contents {
         // entering Agda code
         current := true
-      } else if Js.Re.test_(end_, content) && current.contents {
+      } else if RegExp.test(end_, content) && current.contents {
         // leaving Agda code
         current := false
       }
@@ -231,12 +229,22 @@ let parse = (indices: array<int>, filepath: string, raw: string): array<Diff.t>
   | Agda => Lexer.make(raw)
   }
   /* just lexing, doesn't mess around with raw text, preserves positions */
-  let original =
-    preprocessed
-    |> Lexer.lex(Regex.comment, AgdaRaw, Comment)
-    |> Lexer.lex(Regex.goalBracket, AgdaRaw, GoalBracket)
-    |> Lexer.lex(Regex.goalQuestionMarkRaw, AgdaRaw, GoalQMRaw)
-    |> Lexer.lex(Regex.goalQuestionMark, GoalQMRaw, GoalQM)
+  let original = Lexer.lex(
+    Regex.goalQuestionMark,
+    GoalQMRaw,
+    GoalQM,
+    Lexer.lex(
+      Regex.goalQuestionMarkRaw,
+      AgdaRaw,
+      GoalQMRaw,
+      Lexer.lex(
+        Regex.goalBracket,
+        AgdaRaw,
+        GoalBracket,
+        Lexer.lex(Regex.comment, AgdaRaw, Comment, preprocessed),
+      ),
+    ),
+  )
   let questionMark2GoalBracket = token => {
     /* ? => {!  !} */
 
@@ -265,28 +273,32 @@ let parse = (indices: array<int>, filepath: string, raw: string): array<Diff.t>
 
     /* calculate how much space we have */
     let content: string =
-      Js.Re.exec_(Regex.goalBracketContent, token.content)
-      ->Option.flatMap(result =>
-        Js.Re.captures(result)[1]->Option.map(Js.Nullable.toOption)->Option.flatMap(x => x)
-      )
-      ->Option.getWithDefault("")
+      // Js.Re.exec_(Regex.goalBracketContent, token.content)
+      // ->Option.flatMap(result =>{
+      //   Js.Re.captures(result)[1]->Option.map(Js.Nullable.toOption)->Option.flatMap(x => x)
+      // })
+      // ->Option.getOr("")
+      Regex.goalBracketContent
+      ->RegExp.exec(token.content)
+      ->Option.flatMap(result => result[1]->Option.flatMap(x => x))
+      ->Option.getOr("")
+
     let actualSpaces =
       content
-      ->Js.String.match_(%re("/\s*$/"), _)
+      ->String.match(%re("/\s*$/"))
       ->Option.flatMap(matches =>
         switch matches[0] {
         | None => None
         | Some(None) => None
-        | Some(Some(s)) => Some(Js.String.length(s))
+        | Some(Some(s)) => Some(String.length(s))
         }
       )
-      ->Option.getWithDefault(0)
+      ->Option.getOr(0)
 
     /* make room for the index, if there's not enough space */
     let newContent = if actualSpaces < requiredSpaces {
-      let padding = Js.String.repeat(requiredSpaces - actualSpaces, "")
-
-      Js.String.replaceByRe(%re("/\{!.*!\}/"), "{!" ++ content ++ padding ++ "!}", token.content)
+      let padding = " "->String.repeat(requiredSpaces - actualSpaces)
+      token.content->String.replaceRegExp(%re("/\{!.*!\}/"), "{!" ++ content ++ padding ++ "!}")
     } else {
       token.content
     }
@@ -296,15 +308,16 @@ let parse = (indices: array<int>, filepath: string, raw: string): array<Diff.t>
     {content: newContent, kind: GoalBracket, range: (1, 2)}
   }
 
-  let modified =
-    original
-    |> Lexer.mapOnly(GoalQM, questionMark2GoalBracket)
-    |> Lexer.mapOnly(GoalBracket, adjustGoalBracket)
-  let originalHoles = original->Array.keep(isHole)
-  let modifiedHoles = modified->Array.keep(isHole)
+  let modified = Lexer.mapOnly(
+    GoalBracket,
+    adjustGoalBracket,
+    Lexer.mapOnly(GoalQM, questionMark2GoalBracket, original),
+  )
+  let originalHoles = original->Array.filter(isHole)
+  let modifiedHoles = modified->Array.filter(isHole)
 
   originalHoles
-  ->Array.mapWithIndex((idx, token: Token.t) =>
+  ->Array.mapWithIndex((token: Token.t, idx: int) =>
     switch (modifiedHoles[idx], indices[idx]) {
     | (Some(modifiedHole), Some(index)) =>
       let (start, _) = modifiedHole.range
@@ -318,5 +331,5 @@ let parse = (indices: array<int>, filepath: string, raw: string): array<Diff.t>
     | _ => None
     }
   )
-  ->Array.keepMap(x => x)
+  ->Array.filterMap(x => x)
 }