Re-write the type-checker to make it more extensible

src/ast.d.ts

@@ -61,79 +61,79 @@ export const enum SyntaxKind {
   BoltResumeStatement = 69,
   BoltExpressionStatement = 70,
   BoltParameter = 71,
-  BoltModule = 74,
+  BoltModule = 75,
-  BoltFunctionDeclaration = 76,
+  BoltFunctionDeclaration = 77,
-  BoltVariableDeclaration = 77,
+  BoltVariableDeclaration = 78,
-  BoltPlainImportSymbol = 79,
+  BoltPlainImportSymbol = 80,
-  BoltImportDeclaration = 80,
+  BoltImportDeclaration = 81,
-  BoltTraitDeclaration = 81,
+  BoltTraitDeclaration = 82,
-  BoltImplDeclaration = 82,
+  BoltImplDeclaration = 83,
-  BoltTypeAliasDeclaration = 83,
+  BoltTypeAliasDeclaration = 84,
-  BoltRecordField = 85,
+  BoltRecordField = 86,
-  BoltRecordDeclaration = 86,
+  BoltRecordDeclaration = 87,
-  BoltMacroCall = 88,
+  BoltMacroCall = 89,
-  JSOperator = 91,
+  JSOperator = 92,
-  JSIdentifier = 92,
+  JSIdentifier = 93,
-  JSString = 93,
+  JSString = 94,
-  JSInteger = 94,
+  JSInteger = 95,
-  JSFromKeyword = 95,
+  JSFromKeyword = 96,
-  JSReturnKeyword = 96,
+  JSReturnKeyword = 97,
-  JSTryKeyword = 97,
+  JSTryKeyword = 98,
-  JSFinallyKeyword = 98,
+  JSFinallyKeyword = 99,
-  JSCatchKeyword = 99,
+  JSCatchKeyword = 100,
-  JSImportKeyword = 100,
+  JSImportKeyword = 101,
-  JSAsKeyword = 101,
+  JSAsKeyword = 102,
-  JSConstKeyword = 102,
+  JSConstKeyword = 103,
-  JSLetKeyword = 103,
+  JSLetKeyword = 104,
-  JSExportKeyword = 104,
+  JSExportKeyword = 105,
-  JSFunctionKeyword = 105,
+  JSFunctionKeyword = 106,
-  JSWhileKeyword = 106,
+  JSWhileKeyword = 107,
-  JSForKeyword = 107,
+  JSForKeyword = 108,
-  JSCloseBrace = 108,
+  JSCloseBrace = 109,
-  JSCloseBracket = 109,
+  JSCloseBracket = 110,
-  JSCloseParen = 110,
+  JSCloseParen = 111,
-  JSOpenBrace = 111,
+  JSOpenBrace = 112,
-  JSOpenBracket = 112,
+  JSOpenBracket = 113,
-  JSOpenParen = 113,
+  JSOpenParen = 114,
-  JSSemi = 114,
+  JSSemi = 115,
-  JSComma = 115,
+  JSComma = 116,
-  JSDot = 116,
+  JSDot = 117,
-  JSDotDotDot = 117,
+  JSDotDotDot = 118,
-  JSMulOp = 118,
+  JSMulOp = 119,
-  JSAddOp = 119,
+  JSAddOp = 120,
-  JSDivOp = 120,
+  JSDivOp = 121,
-  JSSubOp = 121,
+  JSSubOp = 122,
-  JSLtOp = 122,
+  JSLtOp = 123,
-  JSGtOp = 123,
+  JSGtOp = 124,
-  JSBOrOp = 124,
+  JSBOrOp = 125,
-  JSBXorOp = 125,
+  JSBXorOp = 126,
-  JSBAndOp = 126,
+  JSBAndOp = 127,
-  JSBNotOp = 127,
+  JSBNotOp = 128,
-  JSNotOp = 128,
+  JSNotOp = 129,
-  JSBindPattern = 130,
+  JSBindPattern = 131,
-  JSConstantExpression = 132,
+  JSConstantExpression = 133,
-  JSMemberExpression = 133,
+  JSMemberExpression = 134,
-  JSCallExpression = 134,
+  JSCallExpression = 135,
-  JSBinaryExpression = 135,
+  JSBinaryExpression = 136,
-  JSUnaryExpression = 136,
+  JSUnaryExpression = 137,
-  JSNewExpression = 137,
+  JSNewExpression = 138,
-  JSSequenceExpression = 138,
+  JSSequenceExpression = 139,
-  JSConditionalExpression = 139,
+  JSConditionalExpression = 140,
-  JSLiteralExpression = 141,
+  JSLiteralExpression = 142,
-  JSReferenceExpression = 142,
+  JSReferenceExpression = 143,
-  JSCatchBlock = 145,
+  JSCatchBlock = 146,
-  JSTryCatchStatement = 146,
+  JSTryCatchStatement = 147,
-  JSExpressionStatement = 147,
+  JSExpressionStatement = 148,
-  JSConditionalStatement = 148,
+  JSConditionalStatement = 149,
-  JSReturnStatement = 149,
+  JSReturnStatement = 150,
-  JSParameter = 150,
+  JSParameter = 151,
-  JSImportStarBinding = 154,
+  JSImportStarBinding = 155,
-  JSImportAsBinding = 155,
+  JSImportAsBinding = 156,
-  JSImportDeclaration = 156,
+  JSImportDeclaration = 157,
-  JSFunctionDeclaration = 157,
+  JSFunctionDeclaration = 158,
-  JSArrowFunctionDeclaration = 158,
+  JSArrowFunctionDeclaration = 159,
-  JSLetDeclaration = 159,
+  JSLetDeclaration = 160,
-  JSSourceFile = 160,
+  JSSourceFile = 161,
 }
 
 
@@ -387,7 +387,7 @@ export interface BoltSourceFile extends SyntaxBase<SyntaxKind.BoltSourceFile> {
 
 export interface BoltQualName extends SyntaxBase<SyntaxKind.BoltQualName> {
   kind: SyntaxKind.BoltQualName;
-  modulePath: BoltIdentifier[];
+  modulePath: BoltIdentifier[] | null;
   name: BoltSymbol;
 }
 
@@ -507,7 +507,7 @@ export interface BoltCaseExpression extends SyntaxBase<SyntaxKind.BoltCaseExpres
 
 export interface BoltBlockExpression extends SyntaxBase<SyntaxKind.BoltBlockExpression> {
   kind: SyntaxKind.BoltBlockExpression;
-  statements: BoltStatement[];
+  elements: BoltFunctionBodyElement[];
 }
 
 export interface BoltConstantExpression extends SyntaxBase<SyntaxKind.BoltConstantExpression> {
@@ -557,6 +557,12 @@ export type BoltDeclaration
   | BoltMacroCall
 
 
+export type BoltTypeDeclaration
+  = BoltTraitDeclaration
+  | BoltTypeAliasDeclaration
+  | BoltRecordDeclaration
+
+
 export const enum BoltDeclarationModifiers {
   Mutable = 1,Public = 2,IsType = 4,IsForeign = 8,}
 
@@ -648,7 +654,7 @@ export interface BoltRecordField extends SyntaxBase<SyntaxKind.BoltRecordField>
 export interface BoltRecordDeclaration extends SyntaxBase<SyntaxKind.BoltRecordDeclaration> {
   kind: SyntaxKind.BoltRecordDeclaration;
   modifiers: BoltDeclarationModifiers;
-  name: BoltQualName;
+  name: BoltIdentifier;
   typeParms: BoltTypeParameter[] | null;
   members: BoltRecordMember[] | null;
 }
@@ -667,6 +673,9 @@ export type BoltSourceElement
   | BoltTypeAliasDeclaration
   | BoltRecordDeclaration
   | BoltMacroCall
+  | BoltTraitDeclaration
+  | BoltTypeAliasDeclaration
+  | BoltRecordDeclaration
 
 
 export interface BoltMacroCall extends SyntaxBase<SyntaxKind.BoltMacroCall> {
@@ -1379,7 +1388,7 @@ export function createBoltParenthesized(text: string, span?: TextSpan | null): B
 export function createBoltBraced(text: string, span?: TextSpan | null): BoltBraced;
 export function createBoltBracketed(text: string, span?: TextSpan | null): BoltBracketed;
 export function createBoltSourceFile(elements: BoltSourceElement[], span?: TextSpan | null): BoltSourceFile;
-export function createBoltQualName(modulePath: BoltIdentifier[], name: BoltSymbol, span?: TextSpan | null): BoltQualName;
+export function createBoltQualName(modulePath: BoltIdentifier[] | null, name: BoltSymbol, span?: TextSpan | null): BoltQualName;
 export function createBoltReferenceTypeExpression(name: BoltQualName, arguments: BoltTypeExpression[] | null, span?: TextSpan | null): BoltReferenceTypeExpression;
 export function createBoltTypeParameter(index: number, name: BoltIdentifier, defaultType: BoltTypeExpression | null, span?: TextSpan | null): BoltTypeParameter;
 export function createBoltBindPattern(name: BoltIdentifier, span?: TextSpan | null): BoltBindPattern;
@@ -1396,7 +1405,7 @@ export function createBoltMatchArm(pattern: BoltPattern, body: BoltExpression, s
 export function createBoltMatchExpression(value: BoltExpression, arms: BoltMatchArm[], span?: TextSpan | null): BoltMatchExpression;
 export function createBoltCase(test: BoltExpression, result: BoltExpression, span?: TextSpan | null): BoltCase;
 export function createBoltCaseExpression(cases: BoltCase[], span?: TextSpan | null): BoltCaseExpression;
-export function createBoltBlockExpression(statements: BoltStatement[], span?: TextSpan | null): BoltBlockExpression;
+export function createBoltBlockExpression(elements: BoltFunctionBodyElement[], span?: TextSpan | null): BoltBlockExpression;
 export function createBoltConstantExpression(value: BoltValue, span?: TextSpan | null): BoltConstantExpression;
 export function createBoltReturnStatement(value: BoltExpression | null, span?: TextSpan | null): BoltReturnStatement;
 export function createBoltResumeStatement(value: BoltExpression, span?: TextSpan | null): BoltResumeStatement;
@@ -1411,7 +1420,7 @@ export function createBoltTraitDeclaration(modifiers: BoltDeclarationModifiers,
 export function createBoltImplDeclaration(modifiers: BoltDeclarationModifiers, name: BoltIdentifier, trait: BoltTypeExpression, typeParams: BoltTypeParameter[] | null, elements: BoltDeclaration[], span?: TextSpan | null): BoltImplDeclaration;
 export function createBoltTypeAliasDeclaration(modifiers: BoltDeclarationModifiers, name: BoltIdentifier, typeParams: BoltTypeParameter[] | null, typeExpr: BoltTypeExpression, span?: TextSpan | null): BoltTypeAliasDeclaration;
 export function createBoltRecordField(name: BoltIdentifier, type: BoltTypeExpression, span?: TextSpan | null): BoltRecordField;
-export function createBoltRecordDeclaration(modifiers: BoltDeclarationModifiers, name: BoltQualName, typeParms: BoltTypeParameter[] | null, members: BoltRecordMember[] | null, span?: TextSpan | null): BoltRecordDeclaration;
+export function createBoltRecordDeclaration(modifiers: BoltDeclarationModifiers, name: BoltIdentifier, typeParms: BoltTypeParameter[] | null, members: BoltRecordMember[] | null, span?: TextSpan | null): BoltRecordDeclaration;
 export function createBoltMacroCall(name: BoltIdentifier, text: string, span?: TextSpan | null): BoltMacroCall;
 export function createJSOperator(text: string, span?: TextSpan | null): JSOperator;
 export function createJSIdentifier(text: string, span?: TextSpan | null): JSIdentifier;
@@ -1546,6 +1555,7 @@ export function isBoltResumeStatement(value: any): value is BoltResumeStatement;
 export function isBoltExpressionStatement(value: any): value is BoltExpressionStatement;
 export function isBoltParameter(value: any): value is BoltParameter;
 export function isBoltDeclaration(value: any): value is BoltDeclaration;
+export function isBoltTypeDeclaration(value: any): value is BoltTypeDeclaration;
 export function isBoltModule(value: any): value is BoltModule;
 export function isBoltFunctionBodyElement(value: any): value is BoltFunctionBodyElement;
 export function isBoltFunctionDeclaration(value: any): value is BoltFunctionDeclaration;

src/checker.ts

@@ -1,343 +1,291 @@
+/**
+ *
+ * ```
+ * mod foo {
+ *   type MyType1 = i32;
+ *   mod bar {
+ *     pub type MyType2 = MyType1;
+ *   }
+ * }
+ * ```
+ *
+ * ```
+ * mod foo {
+ *   let x = 1;
+ *   mod bar {
+ *     fn do_something(y) {
+ *       return x + y;
+ *     }
+ *   }
+ * }
+ * ```
+ *
+ * Note that the `pub`-keyword is not present on `MyType1`.
+ */
 
-import {
+import {Syntax, SyntaxKind, BoltReferenceExpression, BoltDeclaration, BoltSourceFile, BoltSyntax, BoltReferenceTypeExpression, BoltTypeDeclaration} from "./ast";
-  Syntax,
+import {FastStringMap} from "./util";
-  kindToString,
+import {DiagnosticPrinter, E_TYPES_NOT_ASSIGNABLE, E_TYPE_DECLARATION_NOT_FOUND, E_DECLARATION_NOT_FOUND} from "./diagnostics";
-  SyntaxKind,
-  BoltImportDeclaration,
-  BoltPattern,
-  isBoltTypeAliasDeclaration,
-  BoltFunctionBodyElement,
-} from "./ast"
-
-import { FastStringMap, getFullTextOfQualName } from "./util"
-
-export class Type {
-  
-}
-
-export class PrimType extends Type {
-
-}
-
-export class FunctionType extends Type {
-
-  constructor(
-    public paramTypes: Type[],
-    public returnType: Type,
-  ) {
-    super();
-  }
-
-}
-
-export class VariantType extends Type {
-
-  constructor(public elementTypes: Type[]) {
-    super();
-  }
-
-}
-
-export const stringType = new PrimType()
-export const intType = new PrimType()
-export const boolType = new PrimType()
-export const voidType = new PrimType()
-export const anyType = new PrimType()
-export const noneType = new PrimType();
-
-export class RecordType {
-
-  private fieldTypes = new FastStringMap<string, Type>();
-
-  constructor(
-    iterable: IterableIterator<[string, Type]>,
-  ) {
-    for (const [name, type] of iterable) {
-      this.fieldTypes.set(name, type);
-    }
-  }
-
-  hasField(name: string) {
-    return name in this.fieldTypes;
-  }
-
-  getTypeOfField(name: string) {
-    return this.fieldTypes.get(name);
-  }
-
-}
 
 interface SymbolInfo {
-  type: Type | null;
+  declarations: BoltDeclaration[];
-  definitions: Syntax[];
 }
 
-export class Scope {
+interface TypeSymbolInfo {
-
+  declarations: BoltTypeDeclaration[];
-  private symbolsByLocalName = new FastStringMap<string, SymbolInfo>();
-
-  constructor(
-    public originatingNode: Syntax,
-    public parentScope?: Scope | null
-  ) {
-
-  }
-
-  public getSymbolNamed(name: string): SymbolInfo | null {
-    let currScope: Scope | null = this;
-    while (true) {
-      if (currScope.symbolsByLocalName.has(name)) {
-        return currScope.symbolsByLocalName.get(name);
-      }
-      currScope = currScope.parentScope;
-      if (currScope === null) {
-        break;
-      }
-    }
-    return null;
-  }
-
-  public getTypeNamed(name: string): Type | null {
-    const sym = this.getSymbolNamed(name);
-    if (sym === null || !introducesNewType(sym.definitions[0].kind)) {
-      return null;
-    }
-    return sym.type!;
-  }
-
-}
-
-function* map<T, R>(iterable: Iterable<T>, proc: (value: T) => R): IterableIterator<R> {
-  const iterator = iterable[Symbol.iterator]();
-  while (true) {
-    let { done, value }= iterator.next();
-    if (done) {
-      break
-    }
-    yield proc(value)
-  }
-}
-
-function introducesNewType(kind: SyntaxKind): boolean {
-  return kind === SyntaxKind.BoltRecordDeclaration
-      || kind === SyntaxKind.BoltTypeAliasDeclaration;
 }
 
 function introducesNewScope(kind: SyntaxKind): boolean {
-  return kind === SyntaxKind.BoltFunctionDeclaration 
+  return kind === SyntaxKind.BoltSourceFile
+      || kind === SyntaxKind.BoltModule
+      || kind === SyntaxKind.BoltFunctionDeclaration
+      || kind === SyntaxKind.BoltBlockExpression;
+}
+
+function introducesNewTypeScope(kind: SyntaxKind): boolean {
+  return kind === SyntaxKind.BoltModule
       || kind === SyntaxKind.BoltSourceFile;
 }
 
-function getFullName(node: Syntax) {
+type Scope = unknown;
-  let out = []
+type TypeScope = unknown;
-  let curr: Syntax | null = node;
+
-  while (true) {
+function createSymbol(node: BoltDeclaration): SymbolInfo {
-    switch (curr.kind) {
+  return { declarations: [ node ] };
-      case SyntaxKind.BoltIdentifier:
+}
-        out.unshift(curr.text)
+
-        break;
+function createTypeSymbol(node: BoltTypeDeclaration): TypeSymbolInfo {
-      case SyntaxKind.BoltModule:
+  return { declarations: [ node ] };
-        out.unshift(getFullTextOfQualName(curr.name));
-        break;
-      case SyntaxKind.BoltRecordDeclaration:
-        out.unshift(getFullTextOfQualName(curr.name))
-        break;
-    }
-    curr = curr.parentNode;
-    if (curr === null) {
-      break;
-    }
-  }
-  return out.join('.');
 }
 
 export class TypeChecker {
 
-  private symbols = new FastStringMap<string, Type>();
+  constructor(private diagnostics: DiagnosticPrinter) {
-  private types = new Map<Syntax, Type>();
-  private scopes = new Map<Syntax, Scope>();
 
-  private inferTypeFromUsage(bindings: BoltPattern, body: BoltFunctionBodyElement[]) {
-    return anyType;
   }
 
-  private getTypeOfBody(body: BoltFunctionBodyElement[]) {
+  private symbols = new FastStringMap<string, SymbolInfo>();
-    return anyType;
+  private typeSymbols = new FastStringMap<string, TypeSymbolInfo>();
+
+  public checkSourceFile(node: BoltSourceFile): void {
+
+    const refExps = node.findAllChildrenOfKind(SyntaxKind.BoltReferenceExpression);
+    for (const refExp of refExps) {
+      if (this.resolveReferenceExpression(refExp) === null) {
+        this.diagnostics.add({
+          message: E_DECLARATION_NOT_FOUND,
+          args: { name: refExp.name.name.text },
+          severity: 'error',
+          node: refExp,
+        })
+      }
+    }
+
+    const typeRefExps = node.findAllChildrenOfKind(SyntaxKind.BoltReferenceTypeExpression);
+    for (const typeRefExp of typeRefExps) {
+      if (this.resolveTypeReferenceExpression(typeRefExp) === null) {
+        this.diagnostics.add({
+          message: E_TYPE_DECLARATION_NOT_FOUND,
+          args: { name: typeRefExp.name.name.text },
+          severity: 'error',
+          node: typeRefExp,
+        })
+      }
+    }
+
   }
 
-  private createType(node: Syntax): Type {
+  public registerSourceFile(node: BoltSourceFile): void {
+    this.addAllSymbolsInNode(node);
+  }
 
-    console.error(`creating type for ${kindToString(node.kind)}`);
+  private addAllSymbolsInNode(node: BoltSyntax): void {
 
     switch (node.kind) {
 
-      case SyntaxKind.BoltReferenceExpression:
+      case SyntaxKind.BoltSourceFile:
-        return anyType;
+      case SyntaxKind.BoltModule:
-
+        for (const element of node.elements) {
-      case SyntaxKind.BoltConstantExpression:
+          this.addAllSymbolsInNode(element);
-        return node.value.type;
+        }
-
+        break;
-      case SyntaxKind.BoltExpressionStatement:
-        return voidType;
-
-      case SyntaxKind.BoltCallExpression:
-        // TODO
-        return anyType;
 
       case SyntaxKind.BoltFunctionDeclaration:
-        let returnType = anyType;
+      {
-        if (node.returnType !== null) {
+        const scope = this.getScopeSurroundingNode(node);
-          returnType = this.getTypeOfNode(node.returnType)
+        const sym = createSymbol(node);
-        }
+        this.addSymbol(node.name.text, scope, sym);
-        if (node.body !== null) {
+        break;
-          returnType = this.intersectTypes(returnType, this.getTypeOfBody(node.body))
+      }
-        }
-        let paramTypes = node.params.map(param => {
-          let paramType = this.getTypeOfNode(param);
-          if (node.body !== null) {
-            paramType = this.intersectTypes(
-              paramType,
-              this.inferTypeFromUsage(param.bindings, node.body)
-            )
-          }
-          return paramType
-        })
-        return new FunctionType(paramTypes, returnType);
-
-      case SyntaxKind.BoltReferenceTypeExpression:
-        const name = getFullTextOfQualName(node.name);
-        const scope = this.getScope(node);
-        let reffed = scope.getTypeNamed(name);
-        if (reffed === null) {
-          reffed = anyType;
-        }
-        return reffed;
 
       case SyntaxKind.BoltRecordDeclaration:
-
+      {
-        const fullName = getFullName(node);
+        const typeScope = this.getTypeScopeSurroundingNode(node);
-        let type;
+        const typeSym = createTypeSymbol(node);
-
+        this.addTypeSymbol(node.name.text, typeScope, typeSym);
-        if (node.members === null) {
+      }
-          type = new PrimType();
-          this.symbols.set(fullName, type);
-        } else {
-          type = new RecordType(map(node.members, member => ([field.name.text, this.getTypeOfNode(field.type)])));
-          this.symbols.set(fullName, type);
-        }
-
-        return type;
-
-      case SyntaxKind.BoltParameter:
-        if (node.type !== null) {
-          return this.getTypeOfNode(node.type)
-        }
-        return anyType;
-
-      default:
-        throw new Error(`Could not derive type of ${kindToString(node.kind)}`)
 
     }
 
   }
 
-  public getSymbolNamed(name: string) {
+  private addSymbol(name: string, scope: Scope, sym: SymbolInfo): void {
-    if (!this.symbols.has(name)) {
+    this.symbols.set(`${name}@${(scope as any).id}`, sym);
+  }
+
+  private addTypeSymbol(name: string, scope: TypeScope, sym: TypeSymbolInfo): void {
+    this.typeSymbols.set(`${name}@${(scope as any).id}`, sym);
+  }
+
+  public getParentScope(scope: Scope): Scope | null {
+    let node = scope as Syntax;
+    if (node.kind === SyntaxKind.BoltSourceFile) {
       return null;
     }
-    return this.symbols.get(name);
+    node = node.parentNode!;
-  }
-
-  public getTypeOfNode(node: Syntax): Type {
-    if (this.types.has(node)) {
-      return this.types.get(node)!
-    }
-    const newType = this.createType(node)
-    this.types.set(node, newType)
-    return newType;
-  }
-
-  public check(node: Syntax) {
-
-    this.getTypeOfNode(node);
-
-    switch (node.kind) {
-
-      case SyntaxKind.BoltRecordDeclaration:
-      case SyntaxKind.BoltConstantExpression:
-        break;
-
-      case SyntaxKind.BoltExpressionStatement:
-        this.check(node.expression);
-        break;
-
-      case SyntaxKind.BoltCallExpression:
-        this.check(node.operator);
-        for (const operand of node.operands) {
-          this.check(operand);
-        }
-        // TODO check whether the overload matches the referenced operator
-        break;
-
-      case SyntaxKind.BoltFunctionDeclaration:
-        if (node.body !== null) {
-          if (Array.isArray(node.body)) {
-            for (const element of node.body) {
-              this.check(element)
-            }
-          }
-        }
-        break;
-
-      case SyntaxKind.BoltReferenceExpression:
-        // TODO implement this
-        break;
-
-      case SyntaxKind.BoltModule:
-      case SyntaxKind.BoltSourceFile:
-        for (const element of node.elements) {
-          this.check(element)
-        }
-        break;
-
-      default:
-        throw new Error(`Could not type-check node ${kindToString(node.kind)}`)
-
-    }
-
-  }
-
-  public getScope(node: Syntax): Scope {
     while (!introducesNewScope(node.kind)) {
       node = node.parentNode!;
     }
-    if (this.scopes.has(node)) {
+    return node;
-      return this.scopes.get(node)!
-    }
-    const scope = new Scope(node)
-    this.scopes.set(node, scope)
-    return scope
   }
 
-  private intersectTypes(a: Type, b: Type): Type {
+  public getParentTypeScope(scope: TypeScope): TypeScope | null {
-    if (a === noneType || b == noneType) {
+    let node = scope as Syntax;
-      return noneType;
+    if (node.kind === SyntaxKind.BoltSourceFile) {
+      return null;
     }
-    if (b === anyType) {
+    node = node.parentNode!;
-      return a
+    while (!introducesNewTypeScope(node.kind)) {
+      node = node.parentNode!;
     }
-    if (a === anyType) {
+    return node;
-      return b;
+  }
+
+  private getScopeSurroundingNode(node: Syntax): Scope {
+    if (node.kind === SyntaxKind.BoltSourceFile) {
+      return node;
     }
-    if (a instanceof FunctionType && b instanceof FunctionType) {
+    return this.getScopeForNode(node.parentNode);
-      if (a.paramTypes.length !== b.paramTypes.length) {
+  }
-        return noneType;
+
+  private getTypeScopeSurroundingNode(node: Syntax): TypeScope {
+    if (node.kind === SyntaxKind.BoltSourceFile) {
+      return node;
+    }
+    return this.getScopeForNode(node.parentNode);
+  }
+
+  private getScopeForNode(node: Syntax): Scope {
+    if (node.kind === SyntaxKind.BoltSourceFile) {
+      return node;
+    }
+    let currNode = node;
+    while (!introducesNewScope(currNode.kind)) {
+      currNode = currNode.parentNode!;
+    }
+    return currNode;
+  }
+
+  private getTypeScopeForNode(node: Syntax): TypeScope {
+    if (node.kind === SyntaxKind.BoltSourceFile) {
+      return node;
+    }
+    let currNode = node;
+    while (!introducesNewTypeScope(currNode.kind)) {
+      currNode = currNode.parentNode!;
+    }
+    return currNode;
+  }
+
+  private lookupSymbolInScope(name: string, scope: Scope): SymbolInfo | null {
+    const key = `${name}@${(scope as any).id}`;
+    if (!this.symbols.has(key)) {
+      return null;
+    }
+    return this.symbols.get(key);
+  }
+
+  private lookupSymbolInTypeScope(name: string, scope: TypeScope): TypeSymbolInfo | null {
+    const key = `${name}@${(scope as any).id}`;
+    if (!this.typeSymbols.has(key)) {
+      return null;
+    }
+    return this.typeSymbols.get(key);
+  }
+
+  public findSymbolInScopeOf(name: string, scope: Scope): SymbolInfo | null {
+    while (true) {
+      const sym = this.lookupSymbolInScope(name, scope);
+      if (sym !== null) {
+        return sym;
       }
-      const returnType = this.intersectTypes(a.returnType, b.returnType);
+      const parentScope = this.getParentScope(scope);
-      const paramTypes = a.paramTypes.map((_, i) => this.intersectTypes(a.paramTypes[i], b.paramTypes[i]));
+      if (parentScope === null) {
-      return new FunctionType(paramTypes, returnType)
+        break;
+      }
+      scope = parentScope;
     }
-    return noneType;
+    return null;
+  }
+
+  public findSymbolInTypeScopeOf(name: string, scope: TypeScope): TypeSymbolInfo | null {
+    while (true) {
+      const sym = this.lookupSymbolInTypeScope(name, scope);
+      if (sym !== null) {
+        return sym;
+      }
+      const parentTypeScope = this.getParentTypeScope(scope);
+      if (parentTypeScope === null) {
+        break;
+      }
+      scope = parentTypeScope;
+    }
+    return null;
+  }
+
+  public resolveReferenceExpression(node: BoltReferenceExpression): BoltDeclaration | null {
+    let scope = this.getScopeSurroundingNode(node);
+    if (node.name.modulePath !== null) {
+      while (true) {
+        let shouldSearchParentScopes = false;
+        let currScope = scope;
+        for (const name of node.name.modulePath) {
+          const sym = this.lookupSymbolInScope(name.text, currScope);
+          if (sym === null) {
+            shouldSearchParentScopes = true;
+            break;
+          }
+          if (sym.declarations[0].kind !== SyntaxKind.BoltModule) {
+            shouldSearchParentScopes = true;
+            break;
+          }
+          currScope = this.getScopeForNode(sym.declarations[0]);
+        }
+        if (!shouldSearchParentScopes) {
+          scope = currScope;
+          break;
+        }
+        const parentScope = this.getParentScope(scope);
+        if (parentScope === null) {
+          return null;
+        }
+        scope = parentScope;
+      }
+    }
+    const sym = this.findSymbolInScopeOf(node.name.name.text, scope);
+    if (sym === null) {
+      return null;
+    }
+    return sym.declarations[0]!;
+  }
+
+  public resolveTypeReferenceExpression(node: BoltReferenceTypeExpression): BoltTypeDeclaration | null {
+    const typeScope = this.getTypeScopeSurroundingNode(node);
+    const typeSym = this.findSymbolInTypeScopeOf(node.name.name.text, typeScope);
+    if (typeSym === null) {
+      return null;
+    }
+    return typeSym.declarations[0]!;
   }
 
 }

src/common.ts

@@ -0,0 +1,53 @@
+import {
+  BoltFunctionBodyElement,
+  BoltReturnStatement,
+  SyntaxKind,
+  BoltExpression
+} from "./ast";
+
+export type BoltFunctionBody = BoltFunctionBodyElement[];
+
+export function getAllReturnStatements(body: BoltFunctionBody): BoltReturnStatement[] {
+
+  const results: BoltReturnStatement[] = [];
+
+  for (const element of body) {
+    visit(element);
+  }
+
+  return results;
+
+  function visit(node: BoltFunctionBodyElement) {
+    switch (node.kind) {
+      case SyntaxKind.BoltReturnStatement:
+        results.push(node);
+        break;
+      case SyntaxKind.BoltExpressionStatement:
+        visitExpression(node.expression);
+        break;
+    }
+  }
+
+  function visitExpression(node: BoltExpression) {
+    switch (node.kind) {
+      case SyntaxKind.BoltBlockExpression:
+        for (const element of node.statements) {
+          visit(element);
+        }
+        break;
+      case SyntaxKind.BoltMatchExpression:
+        for (const arm of node.arms) {
+          visitExpression(arm.body);
+        }
+        break;
+      case SyntaxKind.BoltCallExpression:
+        visitExpression(node.operator);
+        for (const operand of node.operands) {
+          visitExpression(operand);
+        }
+        break;
+    }
+  }
+
+}
+

src/di.ts

@@ -38,8 +38,8 @@ export class Container {
     }
   }
 
-  private resolve<T>(factory: Factory<T>): T;
+  public resolve<T>(factory: Factory<T>): T;
-  private resolve(serviceId: ServiceID): any {
+  public resolve(serviceId: ServiceID): any {
     return this.singletons.get(serviceId);
   }
 

src/diagnostics.ts

@@ -0,0 +1,37 @@
+
+import chalk from "chalk"
+import {Syntax} from "./ast";
+import {format, MapLike, FormatArg} from "./util";
+
+export const E_TYPE_DECLARATION_NOT_FOUND = "A type declaration named '{name}' was not found."
+export const E_DECLARATION_NOT_FOUND = "Reference to an undefined declaration '{name}'.";
+export const E_TYPES_NOT_ASSIGNABLE = "Types {left} and {right} are not assignable.";
+
+export interface Diagnostic {
+  message: string;
+  severity: string;
+  args?: MapLike<FormatArg>;
+  node?: Syntax;
+}
+
+export class DiagnosticPrinter {
+
+  public hasErrors = false;
+
+  public add(diagnostic: Diagnostic): void {
+    let out = ''
+    switch (diagnostic.severity) {
+      case 'error':
+        this.hasErrors = true;
+        out += chalk.bold.red('error: ');
+    }
+    if (diagnostic.args !== undefined) {
+      out += format(diagnostic.message, diagnostic.args);
+    } else {
+      out += diagnostic.message;
+    }
+    process.stderr.write(out + '\n');
+  }
+
+}
+

src/frontend.ts

@@ -8,7 +8,7 @@ import { Program } from "./program"
 import { TypeChecker } from "./checker"
 import { Evaluator } from "./evaluator"
 import { emit } from "./emitter"
-import { Syntax } from "./ast"
+import { Syntax, BoltSourceFile } from "./ast"
 import { upsearchSync, FastStringMap, getFileStem, getLanguage } from "./util"
 import { Package } from "./package"
 import { verbose, memoize } from "./util"
@@ -18,6 +18,7 @@ import CompileBoltToJSTransform from "./transforms/boltToJS"
 import ConstFoldTransform from "./transforms/constFold"
 import EliminateModulesTransform from "./transforms/eliminateModules"
 import { TransformManager } from "./transforms/index"
+import {DiagnosticPrinter} from "./diagnostics"
 
 const targetExtensions: MapLike<string> = {
   'JS': '.mjs',
@@ -62,12 +63,14 @@ export class Frontend {
 
   public evaluator: Evaluator;
   public checker: TypeChecker;
+  public diagnostics: DiagnosticPrinter;
   public timing: Timing;
   
   private container = new Container();
 
   constructor() {
-    this.checker = new TypeChecker();
+    this.diagnostics = new DiagnosticPrinter();
+    this.checker = new TypeChecker(this.diagnostics);
     this.evaluator = new Evaluator(this.checker);
     this.timing = new Timing();
     this.container.bindSelf(this.evaluator);
@@ -87,6 +90,17 @@ export class Frontend {
 
   public compile(program: Program, target: string) {
 
+    for (const sourceFile of program.getAllSourceFiles()) {
+      this.checker.registerSourceFile(sourceFile as BoltSourceFile);
+    }
+    for (const sourceFile of program.getAllSourceFiles()) {
+      this.checker.checkSourceFile(sourceFile as BoltSourceFile);
+    }
+
+    if (this.diagnostics.hasErrors) {
+      throw new Error(`Compilation failed because of type-checking errors.`);
+    }
+
     switch (target) {
 
       case "JS":

src/parser.ts

@@ -58,6 +58,7 @@ import {
   BoltFunctionBodyElement,
   createBoltSourceFile,
   BoltRecordField,
+  setParents,
 } from "./ast"
 
 import { parseForeignLanguage } from "./foreign"
@@ -168,24 +169,25 @@ export class Parser {
 
   public parseQualName(tokens: BoltTokenStream): BoltQualName {
 
-    const path: BoltIdentifier[] = [];
+    let modulePath = null;
 
-    while (true) {
+    if (tokens.peek(2).kind === SyntaxKind.BoltDot) {
-      const t0 = tokens.peek(2);
+      modulePath = [];
-      if (t0.kind !== SyntaxKind.BoltDot) {
+      while (true) {
-        break;
+        modulePath.push(tokens.get() as BoltIdentifier)
+        tokens.get();
+        const t0 = tokens.peek(2);
+        if (t0.kind !== SyntaxKind.BoltDot) {
+          break;
+        }
       }
-      path.push(tokens.get() as BoltIdentifier)
-      tokens.get();
     }
 
     const name = tokens.get();
-    if (name.kind !== SyntaxKind.BoltIdentifier) {
+    assertToken(name, SyntaxKind.BoltIdentifier);
-      throw new ParseError(name, [SyntaxKind.BoltIdentifier]);
+    const startNode = modulePath !== null ? modulePath[0] : name;
-    }
-    const startNode = path.length > 0 ? path[0] : name;
     const endNode = name;
-    const node = createBoltQualName(path, name, null);
+    const node = createBoltQualName(modulePath, name as BoltIdentifier, null);
     setOrigNodeRange(node, startNode, endNode);
     return node;
   }
@@ -446,19 +448,14 @@ export class Parser {
 
   public parseStatement(tokens: BoltTokenStream): BoltStatement {
     const t0 = tokens.peek();
-    if (t0.kind === SyntaxKind.BoltReturnKeyword) {
+    if (KIND_EXPRESSION_T0.indexOf(t0.kind) !== -1) {
+      return this.parseExpressionStatement(tokens);
+    } else if (t0.kind === SyntaxKind.BoltReturnKeyword) {
       return this.parseReturnStatement(tokens);
     } else if (t0.kind === SyntaxKind.BoltLoopKeyword) {
       return this.parseLoopStatement(tokens);
     } else {
-      try {
+      throw new ParseError(t0, KIND_STATEMENT_T0);
-        return this.parseExpressionStatement(tokens);
-      } catch (e) {
-        if (!(e instanceof ParseError)) {
-          throw e;
-        }
-        throw new ParseError(t0, KIND_STATEMENT_T0);
-      }
     }
   }
 
@@ -519,7 +516,7 @@ export class Parser {
 
     const t1 = tokens.get();
     assertToken(t1, SyntaxKind.BoltIdentifier);
-    const name = createBoltQualName([], t1 as BoltIdentifier);
+    const name = t1 as BoltIdentifier;
 
     let t2 = tokens.peek();
 
@@ -582,6 +579,10 @@ export class Parser {
       if (t0.kind === SyntaxKind.EndOfFile) {
         break;
       }
+      if (t0.kind === SyntaxKind.BoltSemi) {
+        tokens.get();
+        continue;
+      }
       const statement = this.parseStatement(tokens);
       statements.push(statement);
     }
@@ -1192,6 +1193,8 @@ export function parseSourceFile(filepath: string): BoltSourceFile {
   const contents = fs.readFileSync(file.origPath, 'utf8');
   const scanner = new Scanner(file, contents)
   const parser = new Parser();
-  return parser.parseSourceFile(scanner);
+  const sourceFile = parser.parseSourceFile(scanner);
+  setParents(sourceFile);
+  return sourceFile;
 }
 

src/scanner.ts

@@ -122,30 +122,30 @@ function isSymbol(ch: string) {
 
 export class Scanner {
 
-  protected buffer: string[] = [];
+  private buffer: string[] = [];
-  protected scanned: BoltToken[] = [];
+  private scanned: BoltToken[] = [];
-  protected currPos: TextPos;
+  private currPos: TextPos;
-  protected offset = 0;
+  private offset = 0;
 
   constructor(public file: TextFile, public input: string, startPos = new TextPos(0,1,1)) {
     this.currPos = startPos;
   }
 
-  protected readChar() {
+  private readChar() {
     if (this.offset == this.input.length) {
       return EOF
     }
     return this.input[this.offset++]
   }
 
-  protected peekChar(count = 1) {
+  private peekChar(count = 1) {
     while (this.buffer.length < count) {
       this.buffer.push(this.readChar());
     }
     return this.buffer[count - 1];
   }
 
-  protected getChar() {
+  private getChar() {
 
     const ch = this.buffer.length > 0
       ? this.buffer.shift()!
@@ -166,7 +166,7 @@ export class Scanner {
     return ch
   }
 
-  protected takeWhile(pred: (ch: string) => boolean) {
+  private takeWhile(pred: (ch: string) => boolean) {
     let text = this.getChar();
     while (true) {
       const c0 = this.peekChar();
@@ -190,6 +190,12 @@ export class Scanner {
         continue;
       }
 
+      const c1 = this.peekChar(2);
+      if (c0 === '/' && c1 == '/') {
+        this.scanLineComment();
+        continue;
+      }
+
       const startPos = this.currPos.clone()
 
       if (c0 == EOF) {
@@ -338,6 +344,37 @@ export class Scanner {
 
   }
 
+  private assertChar(ch: string): void {
+    const c0 = this.peekChar();
+    if (c0 !== ch) {
+      throw new ScanError(this.file, this.currPos.clone(), ch);
+    }
+    this.getChar();
+  }
+
+  private scanLineComment(): string {
+    let text = '';
+    this.assertChar('/');
+    this.assertChar('/');
+    while (true) {
+      const c0 = this.peekChar();
+      if (c0 === EOF) {
+        break;
+      }
+      if (c0 == '\n') {
+        this.getChar();
+        const c1 = this.peekChar();
+        if (c1 === '\r') {
+          this.getChar();
+        }
+        break;
+      }
+      text += c0
+      this.getChar();
+    }
+    return text;
+  }
+
   public peek(count = 1): BoltToken {
     while (this.scanned.length < count) {
       this.scanned.push(this.scanToken());

src/transforms/boltToJS.ts

@@ -41,7 +41,7 @@ import {
   BoltSourceElement,
 } from "../ast"
 
-import { getFullTextOfQualName, hasPublicModifier, setOrigNodeRange, FastStringMap } from "../util"
+import { hasPublicModifier, setOrigNodeRange } from "../util"
 import { Program, SourceFile } from "../program"
 import { Transformer, TransformManager } from "./index"
 import { assert } from "../util"
@@ -119,8 +119,9 @@ export class BoltToJSTransform implements Transformer {
         );
 
       case SyntaxKind.BoltReferenceExpression:
+        assert(node.name.modulePath === null);
         return createJSReferenceExpression(
-          getFullTextOfQualName(node.name),
+          node.name.name.text,
           node.span,
         );
 

src/transforms/expand.ts

@@ -10,12 +10,9 @@ import {
   BoltMacroCall,
 } from "../ast"
 
-import { TextSpan } from "../text"
 import { TypeChecker, Scope } from "../checker"
-import { ParseError } from "../util"
 import { BoltTokenStream, Parser, isModifierKeyword } from "../parser"
 import { Evaluator, TRUE, FALSE } from "../evaluator"
-import { setOrigNodeRange, createTokenStream } from "../util"
 import { Transformer, TransformManager } from "./index"
 import { inject } from "../di"
 import {SourceFile} from "../program"

src/transforms/index.ts

@@ -1,8 +1,8 @@
 
-import { SourceFile, Program } from "./program"
+import { SourceFile, Program } from "../program"
-import { Container } from "./di"
+import { Container, Newable } from "../di"
-import {Evaluator} from "./evaluator";
+import {Evaluator} from "../evaluator";
-import {TypeChecker} from "./checker";
+import {TypeChecker} from "../checker";
 
 export interface Transformer {
   isApplicable(node: SourceFile): boolean;
@@ -13,10 +13,6 @@ export interface RegisterTransformerOptions {
 
 }
 
-function createInstance<T>(factory: Factory<T>, ...args: any[]): T {
-  return new factory(...args);
-}
-
 export class TransformManager {
 
   private transformers: Transformer[] = [];
@@ -26,7 +22,7 @@ export class TransformManager {
   }
 
   public register(transformerFactory: Newable<Transformer>, options: RegisterTransformerOptions = {}) {
-    const transformer = this.container.createInstance(transformerFactory, this);
+    const transformer = this.container.createInstance(transformerFactory, this) as Transformer;
     this.transformers.push(transformer);
   }
 

src/treegen/ast-template.js

@@ -58,6 +58,8 @@ function isSyntax(value) {
       && value.__NODE_TYPE !== undefined;
 }
 
+let nextNodeId = 1;
+
 function createNode(nodeType) {
   const obj = Object.create(nodeProto);
   Object.defineProperty(obj, '__NODE_TYPE', {
@@ -73,6 +75,11 @@ function createNode(nodeType) {
       return this.__NODE_TYPE.index;
     }
   });
+  Object.defineProperty(obj, 'id', {
+    enumerable: true,
+    configurable: true,
+    value: nextNodeId++,
+  })
   obj.span = null;
   return obj;
 }
@@ -113,7 +120,7 @@ for (const nodeName of Object.keys(NODE_TYPES)) {
 
 exported.setParents = function setParents(node, parentNode = null) {
   node.parentNode = parentNode;
-  for (const child of getChildNodes(node)) {
+  for (const child of node.getChildNodes()) {
     setParents(child, node)
   }
 }

src/types.ts

@@ -0,0 +1,189 @@
+
+import { FastStringMap } from "./util";
+
+enum TypeKind {
+  OpaqueType,
+  AnyType,
+  NeverType,
+  FunctionType,
+  RecordType,
+  VariantType,
+  TupleType,
+}
+
+export type Type
+  = OpaqueType
+  | AnyType
+  | NeverType
+  | FunctionType
+  | RecordType
+  | VariantType
+  | TupleType
+
+abstract class TypeBase {
+  abstract kind: TypeKind;
+}
+
+export class OpaqueType extends TypeBase {
+  kind: TypeKind.OpaqueType = TypeKind.OpaqueType;
+}
+
+export function isOpaqueType(value: any): value is OpaqueType {
+  return value.kind === TypeKind.OpaqueType;
+}
+
+export class AnyType extends TypeBase {
+  kind: TypeKind.AnyType = TypeKind.AnyType;
+}
+
+export function createAnyType(): AnyType {
+  return new AnyType();
+}
+
+export function isAnyType(value: any): value is AnyType {
+  return value.kind === TypeKind.AnyType;
+}
+
+export class NeverType extends TypeBase {
+  kind: TypeKind.NeverType = TypeKind.NeverType;
+}
+
+export function isNeverType(value: any): value is NeverType {
+  return value instanceof NeverType;
+}
+
+export class FunctionType extends TypeBase {
+
+  kind: TypeKind.FunctionType = TypeKind.FunctionType;
+
+  constructor(
+    public paramTypes: Type[],
+    public returnType: Type,
+  ) {
+    super();
+  }
+
+  public getParameterCount(): number {
+    return this.paramTypes.length;
+  }
+
+  public getParamTypeAtIndex(index: number) {
+    if (index < 0 || index >= this.paramTypes.length) {
+      throw new Error(`Could not get the parameter type at index ${index} because the index  was out of bounds.`);
+    }
+    return this.paramTypes[index];
+  }
+
+}
+
+export function isFunctionType(value: any): value is FunctionType {
+  return value instanceof FunctionType;
+}
+
+export class VariantType extends TypeBase {
+
+  kind: TypeKind.VariantType = TypeKind.VariantType;
+
+  constructor(public elementTypes: Type[]) {
+    super();
+  }
+
+  public getOwnElementTypes(): IterableIterator<Type> {
+    return this.elementTypes[Symbol.iterator]();
+  }
+
+}
+
+export function isVariantType(value: any): value is VariantType {
+  return value instanceof VariantType;
+}
+
+export class RecordType {
+
+  kind: TypeKind.RecordType = TypeKind.RecordType;
+
+  private fieldTypes = new FastStringMap<string, Type>();
+
+  constructor(
+    iterable: IterableIterator<[string, Type]>,
+  ) {
+    for (const [name, type] of iterable) {
+      this.fieldTypes.set(name, type);
+    }
+  }
+
+  public hasField(name: string) {
+    return name in this.fieldTypes;
+  }
+
+  public getTypeOfField(name: string) {
+    return this.fieldTypes.get(name);
+  }
+
+}
+
+export function isRecordType(value: any): value is RecordType {
+  return value.kind === TypeKind.RecordType;
+}
+
+export class TupleType extends TypeBase {
+
+  kind: TypeKind.TupleType = TypeKind.TupleType;
+
+  constructor(public elementTypes: Type[]) {
+    super();
+  }
+
+}
+
+export function intersectTypes(a: Type, b: Type): Type {
+  if (isNeverType(a) || isNeverType(b)) {
+    return new NeverType();
+  }
+  if (isAnyType(b)) {
+    return a
+  }
+  if (isAnyType(a)) {
+    return b;
+  }
+  if (isFunctionType(a) && isFunctionType(b)) {
+    if (a.paramTypes.length !== b.paramTypes.length) {
+      return new NeverType();
+    }
+    const returnType = intersectTypes(a.returnType, b.returnType);
+    const paramTypes = a.paramTypes
+      .map((_, i) => intersectTypes(a.paramTypes[i], b.paramTypes[i]));
+    return new FunctionType(paramTypes, returnType)
+  }
+  return new NeverType();
+}
+
+
+export function isTypeAssignable(a: Type, b: Type): boolean {
+  if (isNeverType(a)) {
+    return false;
+  }
+  if (isAnyType(b)) {
+    return true;
+  }
+  if (isOpaqueType(a) && isOpaqueType(b)) {
+    return a === b;
+  }
+  if (a.kind !== b.kind) {
+    return false;
+  }
+  if (isFunctionType(a) && isFunctionType(b)) {
+    if (a.paramTypes.length !== b.paramTypes.length) {
+      return false;
+    }
+    const paramCount = a.getParameterCount();
+    for (let i = 0; i < paramCount; i++) {
+      if (!isTypeAssignable(a.getParamTypeAtIndex(i), b.getParamTypeAtIndex(i))) {
+        return false;
+      }
+    }
+    return true;
+  }
+  throw new Error(`Should not get here.`);
+}
+

src/util.ts

@@ -169,12 +169,11 @@ export function hasPublicModifier(node: BoltDeclaration) {
   return (node.modifiers & BoltDeclarationModifiers.Public) > 0;
 }
 
-export function getFullTextOfQualName(node: BoltQualName) {
+export function toDeclarationPath(node: BoltQualName): string[] {
-  let out = ''
+  if (node.modulePath === null) {
-  for (const element of node.modulePath) {
+    return [ node.name.text ];
-    out += element.text + '.';
   }
-  return out + node.name.text;
+  return [...node.modulePath.map(id => id.text), node.name.text];
 }
 
 export interface Stream<T> {
@@ -451,3 +450,41 @@ export class ScanError extends Error {
   }
 }
 
+export interface MapLike<T> {
+  [key: string]: T;
+}
+
+export type FormatArg = string | Date | number
+
+export function format(message: string, data: MapLike<FormatArg>) {
+
+  let out = ''
+
+  let name = '';
+  let insideParam = false;
+
+  for (const ch of message) {
+    if (insideParam) {
+      if (ch === '}') {
+        out += data[name]!.toString();
+        reset();
+      }
+      name += ch
+    } else {
+      if (ch === '{') {
+        insideParam = true;
+      } else {
+        out += ch;
+      }
+    }
+  }
+
+  return out;
+
+  function reset() {
+    name = '';
+    insideParam = false;
+  }
+
+}
+