Introduce recognizers

src/recognizers.ts

@@ -0,0 +1,70 @@
+import type { CodePoint, CodePointSpan, CodePointString, SourceCursor } from 'source-region';
+
+export type TextMatch =
+| { tag: "match"; span: CodePointSpan; text: string }
+| { tag: "none" };
+
+export namespace TextMatch {
+  export function match(span: CodePointSpan, text: string): TextMatch {
+    return { tag: "match", span, text };
+  }
+
+  export function none(): TextMatch {
+    return { tag: "none" };
+  }
+}
+
+export function consumeWhile(
+  cursor: SourceCursor,
+  predicate: (cp: CodePoint) => boolean,
+): CodePointSpan {
+  const start = cursor.checkpoint();
+
+  while (true) {
+    const cp = cursor.peek();
+    if (cp === undefined || !predicate(cp)) break;
+    cursor.advance();
+  }
+
+  return cursor.spanFrom(start);
+}
+
+export function consumeWhile1(
+  cursor: SourceCursor,
+  predicate: (cp: CodePoint) => boolean,
+): TextMatch {
+  const start = cursor.checkpoint();
+  const span = consumeWhile(cursor, predicate);
+
+  if (span.start === span.end) {
+    cursor.restore(start);
+    return TextMatch.none();
+  }
+
+  return TextMatch.match(span, cursor.slice(span));
+}
+
+export function skipWhile(
+  cursor: SourceCursor,
+  predicate: (cp: CodePoint) => boolean,
+): CodePointSpan {
+  return consumeWhile(cursor, predicate);
+}
+
+export function matchCodePointString(
+  cursor: SourceCursor,
+  pattern: CodePointString,
+): TextMatch {
+  const start = cursor.checkpoint();
+
+  for (const expected of pattern.codePoints) {
+    if (cursor.peek() !== expected) {
+      cursor.restore(start);
+      return TextMatch.none();
+    }
+    cursor.advance();
+  }
+
+  const span = cursor.spanFrom(start);
+  return TextMatch.match(span, cursor.slice(span));
+}