@jfhbrook/citree
v1.0.2
Published
A DSL for generating ASTs in TypeScript
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citree
citree
is a DSL for generating TypeScript AST files. It's inspired by the
Java AST generator
in Crafting Interpreters by
Robert Nystrom.
Install
You can install citree
into your project with npm:
npm i --save-dev @jfhbrook/citree
Usage
The best way to see how citree
works is to look at the
example:
Creating a Specification
First, make an ast.citree
file. That would look something like this:
type Expr in './expr' {
import { TokenKind } from '../tokens'
Unary => op: TokenKind, expr: Expr
Binary => left: Expr, op: TokenKind, right: Expr
Logical => left: Expr, op: TokenKind, right: Expr
Group => expr: Expr
IntLiteral => value: number
RealLiteral => value: number
BoolLiteral => value: boolean
StringLiteral => value: string
PromptLiteral => value: string
NilLiteral!
}
type Cmd in './cmd' {
import { Expr } from './expr'
Cmd => offsetStart: number = -1, offsetEnd: number = -1
Expression => expression: Expr
Print => expression: Expr
Exit => expression: Expr | null
}
type Tree in './index' {
import { Cmd } from './cmd'
CommandGroup => row: number, source: string, commands: Cmd[]
Line => lineNo: number, row: number, source: string, commands: Cmd[]
Input => input: Array<CommandGroup | Line>
Program => lines: Line[]
}
Running citree
Then, run citree
against that file:
npx @jfhbrook/citree -- ast.citree
This will generate two files, expr.ts
and stmt.ts
. Each of these files
will contain a class, a visitor interface, and a series of subclasses
corresponding to the specified types. It will also contain classes
corresponding to each type.
For example, expr.ts
will look like this:
import { TokenKind } from '../tokens';
export interface ExprVisitor<R> {
visitUnaryExpr(node: Unary): R;
visitBinaryExpr(node: Binary): R;
visitLogicalExpr(node: Logical): R;
visitGroupExpr(node: Group): R;
visitIntLiteralExpr(node: IntLiteral): R;
visitRealLiteralExpr(node: RealLiteral): R;
visitBoolLiteralExpr(node: BoolLiteral): R;
visitStringLiteralExpr(node: StringLiteral): R;
visitPromptLiteralExpr(node: PromptLiteral): R;
visitNilLiteralExpr(node: NilLiteral): R;
}
export abstract class Expr {
abstract accept<R>(visitor: ExprVisitor<R>): R;
}
export class Unary extends Expr {
constructor(
public op: TokenKind,
public expr: Expr,
) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitUnaryExpr(this);
}
}
export class Binary extends Expr {
constructor(
public left: Expr,
public op: TokenKind,
public right: Expr,
) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitBinaryExpr(this);
}
}
export class Logical extends Expr {
constructor(
public left: Expr,
public op: TokenKind,
public right: Expr,
) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitLogicalExpr(this);
}
}
export class Group extends Expr {
constructor(public expr: Expr) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitGroupExpr(this);
}
}
export class IntLiteral extends Expr {
constructor(public value: number) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitIntLiteralExpr(this);
}
}
export class RealLiteral extends Expr {
constructor(public value: number) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitRealLiteralExpr(this);
}
}
export class BoolLiteral extends Expr {
constructor(public value: boolean) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitBoolLiteralExpr(this);
}
}
export class StringLiteral extends Expr {
constructor(public value: string) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitStringLiteralExpr(this);
}
}
export class PromptLiteral extends Expr {
constructor(public value: string) {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitPromptLiteralExpr(this);
}
}
export class NilLiteral extends Expr {
constructor() {
super();
}
accept<R>(visitor: ExprVisitor<R>): R {
return visitor.visitNilLiteralExpr(this);
}
}
Using the Generated Files
For a complete example of using the generated files, check out
Matanuska BASIC, which uses citree
to generate its AST.
Testing
You can run current tests with npm:
npm test
This includes an end-to-end test with the example.
License
This project is MIT licensed. For more, see ./LICENSE.