macros

Towards Fearless Macros

13 Nov 2023
featured
programming-languages, macros

Macros are tricky beasts. Most languages—if they have macros at all—usually include a huge “here there be dragons” warning to warn curious would-be macro programmers of the dangers that lurk ahead. What is it about macros that makes them so dangerous and unwieldy? That’s difficult to answer in general: there are many different macro systems with varying degrees of ease-of-use. Moreover, making macros easy to use safely is an open area of research—most languages that have macros don’t have features necessary to implement macros safely. ...

Implementing Type Systems as Macros

14 Aug 2023
featured
computer-science, programming-languages, macros, type-checking

There’s a neat paper Type Systems as Macros by Chang, Knauth, and Greenman [1] that describes how to implement a typed language using an untyped host language and macro expansion. The paper is neat, but I found the code hard to follow—the paper uses a compact notation that’s convenient for print, but not so much for reproducing on one’s own. This post is my attempt to implement and explain in more accessible terms what’s presented in the paper. ...

Writing Racket Macros: define-syntax and phases

19 May 2023
tutorials
computer-science, macros, racket

There are a bunch of different ways of writing a macro in Racket. There are also some tricky things around phases to keep in mind. This is to help me keep them all straight. 3+1 ways to make a macro # This form: (define-syntax-rule (foo args ...) (use args ...)) is equivalent to: (define-syntax foo (syntax-rules () ([foo args ...] (use args ...)))) Which, is in turn equivalent to: (define-syntax foo (λ (stx) (syntax-case stx () [(gensymed-foo args . ...

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