# Re: [racket-users] Y combinator

```I find this
<https://web.archive.org/web/20170813054608/http://mvanier.livejournal.com/2897.html>
(now dead, but archived) blog post on Y both well paced and approachable.```
```
http://mvanier.livejournal.com/2897.html
<https://web.archive.org/web/20170813054608/http://mvanier.livejournal.com/2897.html>

The post's author considers it to be a massively expanded version of Ch 9
from *TLT/TLS.*

I have also suggested Yin Wang's slides on Reinventing the Y-Combinator
<https://www.slideshare.net/yinwang0/reinventing-the-ycombinator>, which
you might find you enjoy.

Best,

JBH

On Sat, Jan 13, 2018 at 11:57 AM, Matthias Felleisen <matth...@ccs.neu.edu>
wrote:

>
> > On Jan 13, 2018, at 11:53 AM, Hendrik Boom <hend...@topoi.pooq.com>
> wrote:
> >
> > On Sat, Jan 13, 2018 at 08:14:30AM -0800, Zelphir Kaltstahl wrote:
> >>
> >> Anyway, I hope to understand how the Y-combinator works with the help of
> >> "The Little Schemer", which I am reading currently. I am not at that
> >> chapter yet. I am taking my time, first thinking through the stuff and
> >> later typing it into the machine and thinking about it again, sometimes
> >> noticing some detail when I type the code and sometimes making a little
> >> experiment with that code. Already on my way through "The Little
> Schemer" I
> >> hit some useful procedures, which helped me with a totally unrelated
> >> problem when coding my blog in Racket. So it's definitely useful.
> >
> > The Y combinator comes from the original lambda calculus, which was a
> > formal system for computational logic and it elicidated how bound and
> > free variables work.
> >
> > But the system had no built-in mechanism for defining a recursive
> > function.
> >
> > Instead, the Y-combinator was invented -- a lamnda expression that
> > enable you to make a recursive function essentially by passing the
> > functiion as an argument to itself.  Receiving itself as a parameter, it
> > was capable of calling its parameter, which was itself.
> >
> > Have fun deciphering the code.  It took me while, too, way back in the
> > 60's.
>
>
> TLL/TLS does not dump the code on the reader. It develops it,
> step by step, w/o any mystery. It is still a serious “reading” exercise
> for most readers and a rather satisfying one I am told. — Matthias
>
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--
JBH

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