feat(parsers/letter): add letter and letters parsers

src/internal/parsers/letter.ts

@@ -0,0 +1,14 @@
+import { Parser } from '../state'
+
+import { regexp } from './regexp'
+
+const LETTER_RE = /\p{Letter}/gu
+const LETTERS_RE = /\p{Letter}+/gu
+
+export function letter(): Parser<string> {
+  return regexp(LETTER_RE, 'letter')
+}
+
+export function letters(): Parser<string> {
+  return regexp(LETTERS_RE, 'letters')
+}

src/parsers.ts

@@ -3,6 +3,7 @@ export * from './internal/parsers/eof'
 export * from './internal/parsers/float'
 export * from './internal/parsers/integer'
 export * from './internal/parsers/lazy'
+export * from './internal/parsers/letter'
 export * from './internal/parsers/nothing'
 export * from './internal/parsers/regexp'
 export * from './internal/parsers/rest'

tests/internal/parsers/letter.spec.ts

@@ -0,0 +1,65 @@
+import { letter, letters } from '@lib/internal/parsers/letter'
+
+import { run, result, should } from '@tests/@helpers'
+
+describe(letter, () => {
+  it('should succeed with an ASCII letter', () => {
+    const actual = run(letter(), 'A')
+    const expected = result('success', 'A')
+
+    should.matchState(actual, expected)
+  })
+
+  it('should succeed with a Unicode letter', () => {
+    const actual = run(letter(), 'Â')
+    const expected = result('success', 'Â')
+
+    should.matchState(actual, expected)
+  })
+
+  it('should fail if given something other than a letter', () => {
+    ;['1', '+', '~', '`', ':', `'`].forEach((tcase) => {
+      const actual = run(letter(), tcase)
+      const expected = result('failure', 'letter')
+
+      should.matchState(actual, expected)
+    })
+  })
+})
+
+describe(letters, () => {
+  it('should succeed with an ASCII letter if given input with a single ASCII letter', () => {
+    const actual = run(letters(), 'A')
+    const expected = result('success', 'A')
+
+    should.matchState(actual, expected)
+  })
+
+  it('should succeed with a Unicode letter if given input with a single Unicode letter', () => {
+    const actual = run(letters(), 'Â')
+    const expected = result('success', 'Â')
+
+    should.matchState(actual, expected)
+  })
+
+  it('should succeed with letters if given input with letters', () => {
+    const actual = run(letters(), 'Âne')
+    const expected = result('success', 'Âne')
+
+    should.matchState(actual, expected)
+  })
+
+  it('should succeed with letters if given input with letters and other symbols', () => {
+    const actual = run(letters(), 'Âne+9000')
+    const expected = result('success', 'Âne')
+
+    should.matchState(actual, expected)
+  })
+
+  it('should fail if given something other than letters', () => {
+    const actual = run(letters(), '9000+Âne')
+    const expected = result('failure', 'letters')
+
+    should.matchState(actual, expected)
+  })
+})

tests/parsers.spec.ts

@@ -11,6 +11,8 @@ it('should expose parsers', () => {
     'integer',
     'int',
     'lazy',
+    'letter',
+    'letters',
     'nothing',
     'nil',
     'regexp',