Writing an Eval Procedure in Scheme?

Posted by Planeman on Stack Overflow See other posts from Stack Overflow or by Planeman
Published on 2010-04-12T22:17:40Z Indexed on 2010/04/12 22:22 UTC
Read the original article Hit count: 217

Filed under:

Scheme

|

eval

|

lisp

|

homework

My problem isn't with the built-in eval procedure but how to create a simplistic version of it. Just for starters I would like to be able to take this in '(+ 1 2) and have it evaluate the expression + where the quote usually takes off the evaluation.

I have been thinking about this and found a couple things that might be useful: Unquote: , (quasiquote) (apply)

My main problem is regaining the value of + as a procedure and not a symbol. Once I get that I think I should just be able to use it with the other contents of the list.

Any tips or guidance would be much appreciated.

© Stack Overflow or respective owner

Related posts about Scheme

About "If.." in Scheme (plt-scheme)

as seen on Stack Overflow - Search for 'Stack Overflow'
I had a pretty simple requirement in my Scheme program to execute more than one statement, in the true condition of a 'if'. . So I write my code, something like this: (if (= 1 1) ((expression1) (expression2)) ; these 2 expressions are to be executed when the condition is true (expression3)… >>> More
Detecting EOF in a Binary File using Scheme

as seen on Stack Overflow - Search for 'Stack Overflow'
(define (read-all-input) (local ((define line (bytes->list (read-bytes 4)))) (if (eof-object? line) empty (cons line (read-all-input))))) (void (read-all-input)) The above code fails because bytes-list expects an argument of type byte string, but is given # >>> More
Scheme: Detecting duplicate elements in a list

as seen on Stack Overflow - Search for 'Stack Overflow'
Does R6RS or Chez Scheme v7.9.4 have a library function to check if a list contains duplicate elements? Alternatively, do either have any built in functionality for sets (which dis-allow duplicate elements)? So far, I've only been able to find an example here. The problem with that is that it doesn't… >>> More
Scheme implementations - what does it mean?

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I'm a beginning student in CS, and my classes are mostly in Java. I'm currently going through "Little Schemer" as a self study, and in the process of finding out how to do that I have found numerous references to "implementations" of Scheme. My question is, what are implementations? Are they… >>> More
Traversing Scheme function as a list

as seen on Stack Overflow - Search for 'Stack Overflow'
Isn't it possible to treat functions in Scheme as any other list? Basically, what I want do to is something like this: (define (foo) "hello") (cdr foo) ; or similar, should return the list ((foo) "hello") I've found a similar discussion about this, and I feel a bit disappointed if this is not… >>> More

Related posts about eval

How to execute "eval" without writing "eval" in JavaScript

as seen on Stack Overflow - Search for 'Stack Overflow'
Here's the deal, we have a big JS library that we want to compress, but YUI compressor doesn't fully compress the code if it finds an "eval" statement, out of fear that it will break something else. That's great and all, but we know exactly what is getting eval'd, so we don't want it to get conservative… >>> More
Can I get the "value" of an arbitrary statement in JavaScript (like eval does, but without eval)

as seen on Stack Overflow - Search for 'Stack Overflow'
In JavaScript is there a way to get the "value" of a statement in the same way that function() { return eval("if (true) { 1 }"); } returns "1"; function() { return if (true) { 1 } } and all similar permutations I've tried are not valid syntax. Is eval just blessed with special powers to determine… >>> More
GNU Make: How to call $(wildcard) within $(eval)

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to create a generic build template for my Makefiles, kind of like they discuss in the eval documentation. I can't seem to get the wildcard function to work within an eval. The basic code I'm having issues with looks like this. SRC_DIR = ./src/ PROG_NAME = test define PROGRAM_template … >>> More
Is it possible to create a generic Util Function to be used in Eval Page

as seen on Stack Overflow - Search for 'Stack Overflow'
I am currently binding a Nullable bit column to a listview control. When you declare a list view item I need to handle the case when the null value is used instead of just true or false. <asp:Checkbox ID="Chk1" runat="server" Checked='<%# HandleNullableBool(Eval("IsUsed")) %>' /> Then… >>> More
Workaround for GNU Make 3.80 eval bug

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to create a generic build template for my Makefiles, kind of like they discuss in the eval documentation. I've run into a known bug with GNU Make 3.80. When $(eval) evaluates a line that is over 193 characters, Make crashes with a "Virtual Memory Exhausted" error. The code I have that… >>> More