waiwai swiftc

1. Writing an
Interpreter in
Swift
@kitasuke

2. Swift Intermediate Language -
Memory Promotion

3. Writing an Interpreter in Go

4. kitasuke/monkey-go

5. Modules
• monkey
• token
• lexer
• parser
• ast
• object
• evaluater
• repl

6. kitasuke/monkey-
swift

7. Modules
• monkey
• Syntax
• Lexer
• Sema
• AST
• REPL

8. Syntax
public enum TokenType {
case unknown, illegal, eof
// Identifiers + literals
case identifier, int
// Operators
case assign, plus, minus, bang, asterisk, slash,
comma, semicolon, lessThan, greaterThan, equal, notEqual
case leftParen, rightParen, leftBrace, rightBrace
// Keywords
case function, `let`, `true`, `false`, `if`, `else`, `return`
}

9. Lexer
let|x|=|5|;
let|identifier|equal|int|semicolon

10. Example
public func nextToken() -> Token {
let tokenType: TokenType
switch character {
case "=": // =
tokenType = .assign
case ";": // ;
tokenType = .semicolon
case let character? where isLetter(character): // let, x
tokenType = .identifier
case let character? where isDigit(character): // 5
tokenType = .int
...
}
...
}

11. Sema
let x = 5;
▿ LetStatement
▿ token : Token
- type : Syntax.TokenType.let
- literal : "let"
▿ name : Identifier
▿ token : Token
- type : Syntax.TokenType.identifier
- literal : "x"
▿ value : IntegerLiteral
▿ token : Token
- type : Syntax.TokenType.int
- literal : "5"
- value : 5

12. Example
private func parseLetStatement() -> LetStatement {
// let
let letToken = currentToken
// x
try setNextToken(expects: .identifier)
let name = Identifier(token: currentToken)
// =
try setNextToken(expects: .assign)
// 5
setNextToken()
let value = try parseExpression()
// ;
if isPeekToken(equalTo: .semicolon) {
setNextToken()
}
return LetStatement(token: letToken, name: name, value: value)
}

13. AST
let x = 5;
▿ Integer
- value : 5

14. Example
public func evaluate(node: Node) throws -> Object {
switch node {
case let program as Program:
return try evaluate(program: program)
case let expressionStatement as ExpressionStatement:
return try evaluate(node: expressionStatement.expression)
case let letStatement as LetStatement:
let value = try evaluate(node: letStatement.value)
return value
...
}
}

15. Demo

16. Writing a Compiler in Go

17. Compilers written in Swift
• swift-min-caml
• trill