diff --git a/src/main.ts b/src/main.ts
index c321126..111bc29 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,4 +1,5 @@
 export { parseDocument } from './parser';
-export type { FoundSyntax, ParseDocumentResult, ParseError } from './parser';
+export type { ParseDocumentResult } from './parser';
+export type { FoundSyntax, ParseError } from './parse_errors';
 export { ConcreteSyntax, Expr } from './syntax';
 export type { ConcreteSyntax as ConcreteSyntaxNode, Expr as ExprNode } from './syntax';
diff --git a/src/new_syntax.ts b/src/new_syntax.ts
new file mode 100644
index 0000000..77a2851
--- /dev/null
+++ b/src/new_syntax.ts
@@ -0,0 +1,60 @@
+import type { CodePointSpan } from 'source-region';
+import type { ParseError } from './parse_errors';
+
+export type ConcreteSyntaxResult =
+| { tag: "valid", value: ValidConcreteSyntax }
+| { tag: "invalid", value: PartialConcreteSyntax }
+
+// The main constraints are
+// - `ValidConcreteSyntax` should be a subtype of `PartialConcreteSyntax`
+// - if `PartialConcreteSyntax` doesn't contain any sort of error nodes, we should be able to coerce it to `ValidConcreteSyntax` without rebuilding the whole tree
+export type ValidConcreteSyntax = Program<{ span: CodePointSpan }, never>
+export type PartialConcreteSyntax = Program<{ span: CodePointSpan }, ConcreteError >
+
+export type ConcreteError = ConcreteErrorNode[] // Can't be empty array.
+export type ConcreteErrorNode = {
+  span: CodePointSpan,
+  error: ParseError,
+  panickedOver?: CodePointSpan,
+}
+
+export type DelimiterToken =
+  | { tag: "open-paren"; span: CodePointSpan }
+  | { tag: "close-paren"; span: CodePointSpan }
+  | { tag: "open-bracket"; span: CodePointSpan }
+  | { tag: "close-bracket"; span: CodePointSpan };
+
+export type Program<Info, Error> = {
+  expressions: Expr<Info, Error>[],
+  error?: Error,
+} & Info
+
+export type Expr<Info, Error> =
+| Literal<Info, Error>
+| List<Info, Error>
+| { tag: "error-expression", error: Error } & Info // This is for errors that don't really correspond to any sort of node. Unknown errors.
+
+export type List<Info, Error> =
+  { tag: "list", open: DelimiterToken, items: ListItem<Info, Error>[], close?: DelimiterToken, error?: Error } & Info
+
+export type ListItem<Info, Error> =
+| Expr<Info, Error>
+| { tag: "error-list-separator", error: Error } & Info
+
+export type Literal<Info, Error> =
+// === number ===
+| { tag: "number", value: number } & Info
+| { tag: "error-number", error: Error } & Info
+// === identifier ===
+| { tag: "identifier", value: Identifier } & Info
+| { tag: "error-identifier", error: Error } & Info
+
+export type Identifier = string
+
+
+
+export namespace ConcreteError {
+  export function single(node: ConcreteErrorNode): ConcreteError {
+    return [node];
+  }
+}
diff --git a/src/parse_errors.ts b/src/parse_errors.ts
new file mode 100644
index 0000000..5599ffb
--- /dev/null
+++ b/src/parse_errors.ts
@@ -0,0 +1,33 @@
+import type { CodePoint, CodePointSpan } from 'source-region';
+
+export type ParseError =
+| {
+    tag: "expected-expression";
+    span: CodePointSpan;
+    found: FoundSyntax;
+  }
+| {
+    tag: "expected-close-paren";
+    span: CodePointSpan;
+    openParen: CodePointSpan;
+    found: FoundSyntax;
+  }
+| {
+    tag: "unexpected-close-paren";
+    span: CodePointSpan;
+  }
+| {
+    tag: "unexpected-code-point";
+    span: CodePointSpan;
+    found: FoundSyntax;
+  }
+| {
+    tag: "invalid-number";
+    span: CodePointSpan;
+    text: string;
+    reason: "unsafe-integer";
+  };
+
+export type FoundSyntax =
+| { tag: "code-point"; value: CodePoint; span: CodePointSpan }
+| { tag: "eof"; span: CodePointSpan };
diff --git a/src/parser.ts b/src/parser.ts
index b967d30..da158f9 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -12,6 +12,7 @@ import type {
   CodePointSpan,
   SourceRegion,
 } from 'source-region';
+import type { FoundSyntax, ParseError } from './parse_errors';
 import { consumeWhile, consumeWhile1, skipWhile } from './recognizers';
 import { ConcreteSyntax } from './syntax';
 
@@ -42,38 +43,6 @@ export type ParseDocumentResult = {
   errors: ParseError[];
 };
 
-export type ParseError =
-| {
-    tag: "expected-expression";
-    span: CodePointSpan;
-    found: FoundSyntax;
-  }
-| {
-    tag: "expected-close-paren";
-    span: CodePointSpan;
-    openParen: CodePointSpan;
-    found: FoundSyntax;
-  }
-| {
-    tag: "unexpected-close-paren";
-    span: CodePointSpan;
-  }
-| {
-    tag: "unexpected-code-point";
-    span: CodePointSpan;
-    found: FoundSyntax;
-  }
-| {
-    tag: "invalid-number";
-    span: CodePointSpan;
-    text: string;
-    reason: "unsafe-integer";
-  };
-
-export type FoundSyntax =
-| { tag: "code-point"; value: CodePoint; span: CodePointSpan }
-| { tag: "eof"; span: CodePointSpan };
-
 export function parseDocument(region: SourceRegion): ParseDocumentResult {
   return new Parser(region).parseDocument();
 }
diff --git a/src/ui/App.tsx b/src/ui/App.tsx
index 7255ea8..5c8103e 100644
--- a/src/ui/App.tsx
+++ b/src/ui/App.tsx
@@ -2,7 +2,7 @@ import { createMemo, createSignal, Show } from 'solid-js';
 import { sourceText } from 'source-region';
 import type { CodePointSpan, SourceRegion, SourceText } from 'source-region';
 import { parseDocument } from '../parser';
-import type { ParseError } from '../parser';
+import type { ParseError } from '../parse_errors';
 import type { ConcreteSyntax } from '../syntax';
 import { spanLabel } from './format';
 import { PaneHeader, PaneSplitter } from './Pane';
diff --git a/src/ui/SyntaxPane.tsx b/src/ui/SyntaxPane.tsx
index faf6353..2e7e325 100644
--- a/src/ui/SyntaxPane.tsx
+++ b/src/ui/SyntaxPane.tsx
@@ -1,7 +1,7 @@
 import { For, Show } from 'solid-js';
 import type { JSX } from 'solid-js';
 import type { CodePointSpan } from 'source-region';
-import type { ParseError } from '../parser';
+import type { ParseError } from '../parse_errors';
 import type { ConcreteSyntax } from '../syntax';
 import { Expr } from '../syntax';
 import { errorDetail, errorLabel, errorTitle } from './format';
diff --git a/src/ui/format.ts b/src/ui/format.ts
index 56be364..63d8cf2 100644
--- a/src/ui/format.ts
+++ b/src/ui/format.ts
@@ -1,5 +1,5 @@
 import type { CodePointSpan } from 'source-region';
-import type { FoundSyntax, ParseError } from '../parser';
+import type { FoundSyntax, ParseError } from '../parse_errors';
 
 export function errorTitle(error: ParseError): string {
   switch (error.tag) {