UI and a Lisp experiment

src/syntax.ts

@@ -0,0 +1,59 @@
+import type { CodePointSpan } from 'source-region';
+
+export type ConcreteSyntax = Expr<{ span: CodePointSpan }>
+
+export type Expr<A> =
+| { tag: "literal", value: Literal } & A
+| { tag: "list", values: Expr<A>[] } & A
+
+export namespace ConcreteSyntax {
+  export function number(value: number, span: CodePointSpan): ConcreteSyntax {
+    return { tag: "literal", value: { tag: "number", value }, span };
+  }
+
+  export function identifier(value: Identifier, span: CodePointSpan): ConcreteSyntax {
+    return { tag: "literal", value: { tag: "identifier", value }, span };
+  }
+
+  export function list(values: ConcreteSyntax[], span: CodePointSpan): ConcreteSyntax {
+    return { tag: "list", values, span };
+  }
+}
+
+export namespace Expr {
+  export function number(value: number): Expr<void> {
+    return { tag: "literal", value: { tag: "number", value } };
+  }
+
+  export function identifier(value: Identifier): Expr<void> {
+    return { tag: "literal", value: { tag: "identifier", value } };
+  }
+
+  export function list(values: Expr<void>[]): Expr<void> {
+    return { tag: "list", values };
+  }
+
+  export function show<A>(e: Expr<A>): string {
+    switch (e.tag) {
+      case "literal":
+        return showLiteral(e.value);
+      case "list":
+        return `(${e.values.map(show).join(" ")})`;
+    }
+  }
+
+  function showLiteral(e: Literal): string {
+    switch (e.tag) {
+      case "number":
+        return `${e.value}`;
+      case "identifier":
+        return `${e.value}`;
+    }
+  }
+}
+
+type Literal =
+| { tag: "number", value: number }
+| { tag: "identifier", value: Identifier }
+
+type Identifier = string