StringLiteral

README.md

@@ -37,7 +37,7 @@ npm run mtsc ./tests/singleVar.ts
 - [ ] Make semicolon a statement ender, not statement separator.
   - Hint: You'll need a predicate to peek at the next token and decide if it's the start of an element.
   - Bonus: Switch from semicolon to newline as statement ender.
-- [ ] Add string literals.
+- [x] Add string literals.
 - [ ] Add let.
   - Then add use-before-declaration errors in the checker.
   - Finally, add an ES2015 -> ES5 transform that transforms `let` to `var`.
@@ -50,3 +50,6 @@ npm run mtsc ./tests/singleVar.ts
 - [ ] Add an ES5 transformer that converts let -> var.
 - [ ] Add function declarations and function calls.
 - [ ] Add arrow functions with an appropriate transform in ES5.
+- [ ] Add support for the lexer to report errors
+  - report unterminated string literal error
+- [ ] Refactor: rename `Literal` to `NumericLiteral`

baselines/reference/singleTypedVar.errors.baseline

@@ -2,5 +2,9 @@
   {
     "pos": 17,
     "message": "Cannot assign initialiser of type 'number' to variable with declared type 'string'."
+  },
+  {
+    "pos": 41,
+    "message": "Cannot assign initialiser of type 'string' to variable with declared type 'number'."
   }
 ]

baselines/reference/singleTypedVar.js.baseline

@@ -1 +1 @@
-"var s = 1"
+"var s = 1;\nvar n = 'test'"

baselines/reference/singleTypedVar.tree.baseline

@@ -5,6 +5,12 @@
         "kind": "Var",
         "pos": 3
       }
+    ],
+    "n": [
+      {
+        "kind": "Var",
+        "pos": 22
+      }
     ]
   },
   "statements": [
@@ -23,6 +29,22 @@
         "value": 1
       }
     },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "n"
+      },
+      "typename": {
+        "kind": "Identifier",
+        "text": "number"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "test",
+        "isSingleQuote": true
+      }
+    },
     {
       "kind": "EmptyStatement"
     }

baselines/reference/stringLiteral.errors.baseline

@@ -0,0 +1 @@
+[]

baselines/reference/stringLiteral.js.baseline

@@ -0,0 +1 @@
+"var singleQuote = 'singleQuote';\nvar doubleQuote = \"doubleQuote\";\nvar escapedSingleQuote = 'escapedSingle\\'Quote';\nvar escapedDoubleQuote = \"escapedDouble\\\"Quote\";\nvar escapedB = 'escaped\\nB';\nvar escapedT = 'escaped\\nT';\nvar escapedN = 'escaped\\nN';\nvar escapedR = 'escaped\\nR'"

baselines/reference/stringLiteral.tree.baseline

@@ -0,0 +1,153 @@
+{
+  "locals": {
+    "singleQuote": [
+      {
+        "kind": "Var",
+        "pos": 3
+      }
+    ],
+    "doubleQuote": [
+      {
+        "kind": "Var",
+        "pos": 36
+      }
+    ],
+    "escapedSingleQuote": [
+      {
+        "kind": "Var",
+        "pos": 69
+      }
+    ],
+    "escapedDoubleQuote": [
+      {
+        "kind": "Var",
+        "pos": 118
+      }
+    ],
+    "escapedB": [
+      {
+        "kind": "Var",
+        "pos": 167
+      }
+    ],
+    "escapedT": [
+      {
+        "kind": "Var",
+        "pos": 196
+      }
+    ],
+    "escapedN": [
+      {
+        "kind": "Var",
+        "pos": 225
+      }
+    ],
+    "escapedR": [
+      {
+        "kind": "Var",
+        "pos": 254
+      }
+    ]
+  },
+  "statements": [
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "singleQuote"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "singleQuote",
+        "isSingleQuote": true
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "doubleQuote"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "doubleQuote",
+        "isSingleQuote": false
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "escapedSingleQuote"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "escapedSingle'Quote",
+        "isSingleQuote": true
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "escapedDoubleQuote"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "escapedDouble\"Quote",
+        "isSingleQuote": false
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "escapedB"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "escaped\nB",
+        "isSingleQuote": true
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "escapedT"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "escaped\nT",
+        "isSingleQuote": true
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "escapedN"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "escaped\nN",
+        "isSingleQuote": true
+      }
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "escapedR"
+      },
+      "init": {
+        "kind": "StringLiteral",
+        "value": "escaped\nR",
+        "isSingleQuote": true
+      }
+    },
+    {
+      "kind": "EmptyStatement"
+    }
+  ]
+}

src/check.ts

@@ -58,6 +58,8 @@ export function check(module: Module) {
         return errorType;
       case Node.Literal:
         return numberType;
+      case Node.StringLiteral:
+        return stringType;
       case Node.Assignment:
         const v = checkExpression(expression.value);
         const t = checkExpression(expression.name);

src/emit.ts

@@ -1,5 +1,22 @@
 import { Statement, Node, Expression } from './types';
 
+const singleQuoteRegex = /[\\\'\t\v\f\b\r\n]/g;
+const doubleQuoteRegex = /[\\\"\t\v\f\b\r\n]/g;
+
+const escapedCharsMap = new Map(
+  Object.entries({
+    '\t': '\\t',
+    '\v': '\\v',
+    '\f': '\\f',
+    '\b': '\\b',
+    '\r': '\\r',
+    '\n': '\\n',
+    '\\': '\\\\',
+    '"': '\\"',
+    "'": "\\'",
+  }),
+);
+
 export function emit(statements: Statement[]) {
   return statements.map(emitStatement).join(';\n');
 }
@@ -26,7 +43,22 @@ function emitExpression(expression: Expression): string {
       return expression.text;
     case Node.Literal:
       return '' + expression.value;
+    case Node.StringLiteral:
+      return expression.isSingleQuote
+        ? `'${escapeString(expression.value, true)}'`
+        : `"${escapeString(expression.value, false)}"`;
     case Node.Assignment:
       return `${expression.name.text} = ${emitExpression(expression.value)}`;
   }
 }
+
+function escapeString(string: string, isSingleQuote: boolean) {
+  return string.replace(
+    isSingleQuote ? singleQuoteRegex : doubleQuoteRegex,
+    replacement,
+  );
+}
+
+function replacement(char: string) {
+  return escapedCharsMap.get(char) || char;
+}

src/lex.ts

@@ -1,4 +1,4 @@
-import { Token, Lexer } from './types';
+import { Token, Lexer, CharCodes } from './types';
 
 const keywords = {
   function: Token.Function,
@@ -11,12 +11,14 @@ export function lex(s: string): Lexer {
   let pos = 0;
   let text = '';
   let token = Token.BOF;
+  let firstChar: string;
 
   return {
     scan,
     token: () => token,
     pos: () => pos,
     text: () => text,
+    isSingleQuote: () => firstChar === "'",
   };
 
   function scan() {
@@ -40,6 +42,10 @@ export function lex(s: string): Lexer {
         text in keywords
           ? keywords[text as keyof typeof keywords]
           : Token.Identifier;
+    } else if (['"', "'"].includes(s.charAt(pos))) {
+      firstChar = s.charAt(pos);
+      text = scanString();
+      token = Token.String;
     } else {
       pos++;
       switch (s.charAt(pos - 1)) {
@@ -62,6 +68,64 @@ export function lex(s: string): Lexer {
   function scanForward(pred: (x: string) => boolean) {
     while (pos < s.length && pred(s.charAt(pos))) pos++;
   }
+
+  function scanString() {
+    const quote = s.charCodeAt(pos);
+    pos++;
+
+    let stringValue = '';
+    let start = pos;
+
+    while (true) {
+      if (pos >= s.length) {
+        // report unterminated string literal error
+      }
+
+      const char = s.charCodeAt(pos);
+
+      if (char === quote) {
+        stringValue += s.slice(start, pos);
+        pos++;
+        break;
+      }
+
+      if (char === CharCodes.backslash) {
+        stringValue += s.slice(start, pos);
+        stringValue += scanEscapeSequence();
+        start = pos;
+        continue;
+      }
+
+      pos++;
+    }
+
+    return stringValue;
+  }
+
+  function scanEscapeSequence() {
+    pos++;
+    const char = s.charCodeAt(pos);
+    pos++;
+
+    switch (char) {
+      case CharCodes.b:
+        return '\b';
+      case CharCodes.t:
+        return '\t';
+      case CharCodes.n:
+        return '\n';
+      case CharCodes.r:
+        return '\r';
+      case CharCodes.singleQuote:
+        // prettier-ignore
+        return "\'";
+      case CharCodes.doubleQuote:
+        // prettier-ignore
+        return '\"';
+      default:
+        return String.fromCharCode(char);
+    }
+  }
 }
 
 export function lexAll(s: string) {

src/parse.ts

@@ -38,6 +38,13 @@ export function parse(lexer: Lexer): Module {
       return { kind: Node.Identifier, text: lexer.text(), pos };
     } else if (tryParseToken(Token.Literal)) {
       return { kind: Node.Literal, value: +lexer.text(), pos };
+    } else if (tryParseToken(Token.String)) {
+      return {
+        kind: Node.StringLiteral,
+        value: lexer.text(),
+        pos,
+        isSingleQuote: lexer.isSingleQuote(),
+      };
     }
     error(
       pos,