53 lines
2.7 KiB
Markdown
53 lines
2.7 KiB
Markdown
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I've been working my way through a Lisp textbook, *Lisp In Small
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Pieces*, by Christian Quinnec. It was originally written in French and
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is not that well known among English-speaking Lisperati, not in
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comparison to the Wizard book or Paul Graham's *On Lisp*, but what
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caught my attention was how it really was in *small* pieces. Each
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chapter ended with an interpreter described, sometimes in code,
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sometimes in text; if you were smart enough, you could actually piece
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the whole thing together and see how it worked.
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I decided to make things hard for myself. Since I'm *not* a Lisperati
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(although I may well and truly be seduced by Hy), I decided to make
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things hard for myself by writing the interpreter in Coffeescript. Most
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Lisp books assume you have a Lisp handy, and Quinnec's examples are fine
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and dandy on many variants of Scheme, but for a fun time I decided to
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write it in something else. Raganwald claims Javascript "is a Lisp,"
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and if that's so it ought to be good enough to write a Lisp in it.
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I mean, it's obviously been done before. I tried once before but got
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lost. *LiSP* does me the favor of keeping me on track.
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You can see all my sourcecode at <a
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href="https://github.com/elfsternberg/LispInSmallPieces">Github: Lisp In
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Small Pieces</a>.
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Chapter 1 contains the base interpreter. It also contains a
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hand-written Lisp reader, and refers to another project I have on
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GitHub, <a
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href="https://github.com/elfsternberg/cons-lists">cons-lists</a>, which
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is exactly what it sounds like, a singly-linked list implementation in
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Javascript, using nested Javascript arrays as the base. The base
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interpreter is very primitive-- you can't even create new variable names
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in the global namespace! Although you can shadow them using lambdas, so
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it's pretty much bog standard Lambda Calculus.
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Chapter "Lambda 1" contains a continuation-passing variant of the
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interpreter from Chapter 1. It's basically a facile reading of
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Lisperator's λ-language intepreter, with my own parser front-end and
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some CPS style. It passes all the tests, but it's a distraction.
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Chapter 3 contains the same interpreter, only using the architecture
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Quinnec describes in Chapter 3 of his book.
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Chapter 2 describes a number of different methodologies for binding,
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scoping, and namespaces. The material is interesting but I didn't
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pursue writing the various interpreters. I "got" what Quinnec was
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saying, and if I'm ever interested in writing something with scoping
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rules outside of the lexical scopes with which I'm familiar, I might
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revisit the material.
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The next step will be to add functions to the Chapter 3 interpreter to
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do the various continuation management games, like call/cc, throw/catch,
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and so forth. Because *those*, I feel I need to understand.
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