EmptyStatement

README.md

@@ -33,7 +33,7 @@ npm run mtsc ./tests/singleVar.ts
 
 ## Exercises
 
-- [ ] Add EmptyStatement.
+- [x] Add EmptyStatement.
 - [ ] 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.

baselines/reference/emptyStatement.errors.baseline

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

baselines/reference/emptyStatement.js.baseline

@@ -0,0 +1 @@
+"var x = 1;\nvar y = 2"

baselines/reference/emptyStatement.tree.baseline

@@ -0,0 +1,54 @@
+{
+  "locals": {
+    "x": [
+      {
+        "kind": "Var",
+        "pos": 3
+      }
+    ],
+    "y": [
+      {
+        "kind": "Var",
+        "pos": 22
+      }
+    ]
+  },
+  "statements": [
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "x"
+      },
+      "typename": {
+        "kind": "Identifier",
+        "text": "number"
+      },
+      "init": {
+        "kind": "Literal",
+        "value": 1
+      }
+    },
+    {
+      "kind": "EmptyStatement"
+    },
+    {
+      "kind": "Var",
+      "name": {
+        "kind": "Identifier",
+        "text": "y"
+      },
+      "typename": {
+        "kind": "Identifier",
+        "text": "number"
+      },
+      "init": {
+        "kind": "Literal",
+        "value": 2
+      }
+    },
+    {
+      "kind": "EmptyStatement"
+    }
+  ]
+}

baselines/reference/redeclare.tree.baseline

@@ -29,6 +29,9 @@
         "kind": "Literal",
         "value": 2
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

baselines/reference/singleIdentifier.tree.baseline

@@ -7,6 +7,9 @@
         "kind": "Identifier",
         "text": "x"
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

baselines/reference/singleTypedVar.tree.baseline

@@ -22,6 +22,9 @@
         "kind": "Literal",
         "value": 1
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

baselines/reference/singleVar.tree.baseline

@@ -18,6 +18,9 @@
         "kind": "Literal",
         "value": 1
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

baselines/reference/twoStatements.tree.baseline

@@ -32,6 +32,9 @@
           "value": 2
         }
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

baselines/reference/twoTypedStatements.tree.baseline

@@ -36,6 +36,9 @@
           "value": 2
         }
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

baselines/reference/typeAlias.tree.baseline

@@ -192,6 +192,9 @@
         "kind": "Identifier",
         "text": "Net"
       }
+    },
+    {
+      "kind": "EmptyStatement"
     }
   ]
 }

src/check.ts

@@ -13,6 +13,7 @@ import { resolve } from './bind';
 const stringType: Type = { id: 'string' };
 const numberType: Type = { id: 'number' };
 const errorType: Type = { id: 'error' };
+const emptyType: Type = { id: 'empty' };
 
 function typeToString(type: Type) {
   return type.id;
@@ -41,6 +42,8 @@ export function check(module: Module) {
         return t;
       case Node.TypeAlias:
         return checkType(statement.typename);
+      case Node.EmptyStatement:
+        return emptyType;
     }
   }
 

src/emit.ts

@@ -1,7 +1,7 @@
 import { Statement, Node, Expression } from './types';
 
 export function emit(statements: Statement[]) {
-  return statements.map(emitStatement).join(';\n');
+  return statements.filter(Boolean).map(emitStatement).join(';\n');
 }
 
 function emitStatement(statement: Statement): string {
@@ -15,6 +15,8 @@ function emitStatement(statement: Statement): string {
       )}`;
     case Node.TypeAlias:
       return `type ${statement.name.text} = ${statement.typename.text}`;
+    case Node.EmptyStatement:
+      return '';
   }
 }
 

src/parse.ts

@@ -9,6 +9,8 @@ import {
 } from './types';
 import { error } from './error';
 
+const emptyTokens = [Token.EOF, Token.Semicolon];
+
 export function parse(lexer: Lexer): Module {
   lexer.scan();
   return parseModule();
@@ -69,6 +71,8 @@ export function parse(lexer: Lexer): Module {
       parseExpected(Token.Equals);
       const typename = parseIdentifier();
       return { kind: Node.TypeAlias, name, typename, pos };
+    } else if (emptyTokens.includes(lexer.token())) {
+      return { kind: Node.EmptyStatement };
     }
     return { kind: Node.ExpressionStatement, expr: parseExpression(), pos };
   }

src/transform.ts

@@ -16,6 +16,8 @@ function typescript(statements: Statement[]) {
         return [{ ...statement, typename: undefined }];
       case Node.TypeAlias:
         return [];
+      case Node.EmptyStatement:
+        return [];
     }
   }
 }

src/types.ts

@@ -29,6 +29,7 @@ export enum Node {
   ExpressionStatement,
   Var,
   TypeAlias,
+  EmptyStatement,
 }
 
 export type Error = {
@@ -58,7 +59,7 @@ export type Assignment = Location & {
   value: Expression;
 };
 
-export type Statement = ExpressionStatement | Var | TypeAlias;
+export type Statement = ExpressionStatement | Var | TypeAlias | EmptyStatement;
 
 export type ExpressionStatement = Location & {
   kind: Node.ExpressionStatement;
@@ -78,6 +79,10 @@ export type TypeAlias = Location & {
   typename: Identifier;
 };
 
+export type EmptyStatement = {
+  kind: Node.EmptyStatement;
+};
+
 export type Declaration = Var | TypeAlias; // plus others, like function
 
 export type Symbol = {

tests/emptyStatement.ts

@@ -0,0 +1 @@
+var x: number = 1;;var y: number = 2;