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Frame from Lecture 7A: Metacircular Evaluator, Part 1 Plays via YouTube's privacy-enhanced embed

Lecture 7A: Metacircular Evaluator, Part 1

17 videos recommended on HN
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1 HN user recommended this lecture1 month2020–2023 score 1.5
Years with an HN recommendation, 2007–2026

HN holds the SICP lectures up as joyful classics, and this lecture as the moment the evaluator is revealed.

Lecture 7A from MIT 6.001 (SICP) by Abelson and Sussman introduces the metacircular evaluator, a Scheme interpreter written in Scheme. It shows how evaluating a program is itself a program.

“But mostly it just makes me happy - it's infectious and weird.” (HN, 2020)

1 strong recommendations · 2 citations · Lectures · intermediate

3 Hacker News comments

From the HN archive; up to 20 kept per video, favoring different commenters. Recommendations first.

@mrspeaker Jun 2020 Strongly recommends
on HN thread MIT 6.001 Structure and Interpretation (1986) [video]
I re-watch this course every bunch of years, and every time I get something different from it. But mostly it just makes me happy - it's infectious and weird. Especially the "revelation" (spoiler!) [this video]
SICP lecture revealing the metacircular evaluator, joyful to rewatch

Citations, criticism and jokes

@prezjordan Jul 2021 Cites it
on HN thread Ink programming language
Read more
I learned best in Scheme because you don't need to parse your input and can just evaluate a tree[0] (Parsing is, in my opinion, the most boring part about writing an interpreter!) Chapter 7 of Crafting Interpreters lays out how an evaluator works in a pretty clean way [1]. I've also blogged about evaluating ASTs in JavaScript [2] Lastly, Gary Bernhardt took it a step further and instead of "evaluating" code, "compiled" it to JavaScript (this tutorial uses Ruby) [3]. Very much a mind-blown moment for me. Have fun!! Writing interpreters remains one of my favorite things to do when learning a new programming language. [0] [this video] [1] [link] [2] [link] [3] [link]
Shows evaluating a tree directly in Scheme

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