# Where can I find the definition of eq? procedure **URL:** \ **Category:** Questions & Answers\ **Tags:** question\ **Created:** [April 7, 2022, 4:55am UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856 "2022-04-07T04:55:44Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![otlk](https://avatars.discourse-cdn.com/v4/letter/o/dfb087/32.png) [@otlk](https://racket.discourse.group/u/otlk)\ **Post date:** [April 7, 2022, 4:55am UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856/1 "2022-04-07T04:55:44Z")
I am referring to the eq? procedure that is built into racket [link to racket docs](https://docs.racket-lang.org/reference/Equality.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29) Things I have already tried 1. The solution suggested [here](https://racket.discourse.group/t/how-to-find-the-definition-of-functions/645) does not appear to work in my case. On right clicking eq? identifier the context menu item "Open defining file" does not appear. 2. I downloaded the latest racket source code and used silver searcher but could not find a helpful definition for eq? 2.1 ag -A 10 "define (eq?" returned no results 2.2 ag -A 10 "define eq?" did not return a helpful result Thank you Any help is appreciated ---
**Author:** ![ryanc](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/ryanc/32/71_2.png) [@ryanc](https://racket.discourse.group/u/ryanc)\ **Post date:** [April 7, 2022, 11:17am UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856/2 "2022-04-07T11:17:42Z")
The `eq?` operation is handled specially by the compiler, when it occurs in operator position and is applied to exactly two arguments. The definition you found wraps that operation as a function, which handles the other cases, like maybe `(apply eq? some-list)`. The compiler's handling of `eq?` is partly in racket/src/ChezScheme/s/cpprim.ss: ``` (define-inline 2 eq? [(e1 e2) (or (eqvop-null-fptr e1 e2) (relop-length RELOP= e1 e2) (%inline eq? ,e1 ,e2))]) ``` The first two cases are optimizations for certain patterns of `eq?` comparisons. The first seems related to foreign function pointer comparisons. The second one seems to be optimizing expressions like `(> (length lst) 1)` to avoid the call to `length`. If neither optimization applies, the third case is used: `(%inline eq? _ _)`. I think (but I'm not sure) that `%inline` cooperates with `define-instruction`, so this would use the implementation of `eq?` defined for the specific architecture being used. For example, in racket/src/ChezScheme/s/x86\_64.ss there is ``` (define-instruction pred (eq? u< < > <= >=) ....) ``` which emits machine code for comparisons depending on whether the arguments are immediates or in registers or memory. ---
**Author:** ![alexh](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/alexh/32/315_2.png) [@alexh](https://racket.discourse.group/u/alexh)\ **Post date:** [April 7, 2022, 11:19am UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856/3 "2022-04-07T11:19:32Z")
You found the actual definition of the `eq?` function: ```scheme (define eq? (lambda (x y) (eq? x y))) ``` What happens is that, first the compiler learns how to generate machine code for expressions such as `(eq? x y)`, this is processor specific and for X86-64 it happens here: [racket/x86\_64.ss at e028f252da859759100f9248230bdc4e203a6684 · racket/racket · GitHub](https://github.com/racket/racket/blob/e028f252da859759100f9248230bdc4e203a6684/racket/src/ChezScheme/s/x86_64.ss#L716) Next, the procedure `eq?` is defined having the expression `(eq? x y)` as its body, but the compiler already knows what code to generate for that expression. Alex. ---
**Author:** ![otlk](https://avatars.discourse-cdn.com/v4/letter/o/dfb087/32.png) [@otlk](https://racket.discourse.group/u/otlk)\ **Post date:** [April 9, 2022, 4:51am UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856/4 "2022-04-09T04:51:43Z")
I tried to grok the definition of define-instruction at [ChezScheme/x86\_64.ss at 0d5ec1da706fc4e08acca748284963fd286eed59 · cisco/ChezScheme · GitHub](https://github.com/cisco/ChezScheme/blob/0d5ec1da706fc4e08acca748284963fd286eed59/s/x86_64.ss#L234) However, it appears to be a very complex and long definition. Is the definition of define-instruction hand written or computer generated? Are there tests or documentation for define-instruction that will help me understand what it does? I could not find anything at [Index](https://scheme.com/tspl4/tspl_1.html#./tspl:h0) @alexh and @ryanc I don't know enough about compilers and CPUs to understand your respective answers. I don't know which answer to mark as a solution, maybe the forum moderators can select one. ---
**Author:** ![jbclements](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/jbclements/32/11_2.png) [@jbclements](https://racket.discourse.group/u/jbclements)\ **Post date:** [April 9, 2022, 5:04pm UTC](https://racket.discourse.group/t/where-can-i-find-the-definition-of-eq-procedure/856/5 "2022-04-09T17:04:31Z")
I can't help but wonder what your goal here is, just to make sure we haven't missed something obvious. Are you trying to figure out the low-level details of how something like `eq?` is implemented, or are you trying to figure out how to use it? If you're interested in low level details, it sounds like you might want to take a look at Jeremy Siek's book, Essentials of Compilation: > **[book.pdf](https://www.dropbox.com/s/ktdw8j0adcc44r0/book.pdf?dl=1)** This book dives into the nanopass architecture that is the foundation for Chez Scheme. But ... i have the feeling that this is an x-y problem, and there's something else that might be more helpful to you.