<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=utf-8"> <META content="MSHTML 6.00.6000.16674" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY> <DIV><FONT face="Courier New" size=2>Why bother about eval? Nevertheless:</FONT></DIV> <DIV><FONT face="Courier New"><FONT size=2><FONT face="Courier New" size=2></FONT></FONT></FONT> </DIV> <DIV><FONT face="Courier New" size=2>From: </FONT><A href="http://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-17.html#node_idx_1266"><FONT face="Courier New" size=2>http://www.r6rs.org/final/html/r6rs-lib/r6rs-lib-Z-H-17.html#node_idx_1266</FONT></A></DIV> <DIV><FONT face="Courier New"><FONT size=2><FONT face="Courier New" size=2></FONT></FONT></FONT> </DIV> <DIV><FONT face="Courier New" size=2>QUOTE</FONT></DIV> <DIV align=left><FONT face="Courier New" size=2>(</FONT><A name=node_idx_1266></A><FONT face="Courier New" size=2>eval expression environment)    procedure </FONT></DIV> <DIV><FONT face="Courier New" size=2>Evaluates expression in the specified environment and returns its value. Expression must be a syntactically valid Scheme expression represented as a datum value, and environment must be an </FONT><A name=node_idx_1268></A><FONT face="Courier New" size=2>environment, which can be created using the environment procedure described below.</FONT></DIV> <DIV><FONT face="Courier New" size=2>If the first argument to eval is determined not to be a syntactically correct expression, then eval must raise an exception with condition type &syntax. Specifically, if the first argument to eval is a definition or a splicing begin form containing a definition, it must raise an exception with condition type &syntax. </FONT></DIV> <DIV><FONT face="Courier New" size=2>UNQUOTE</FONT></DIV> <DIV> </DIV> <DIV><FONT face="Courier New" size=2>See also: <A href="http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-4.html#node_idx_52">http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-4.html#node_idx_52</A></FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>In #lang scheme and mzscheme and pretty-big the value of a procedure is that procedure. There is #!r6rs though, but:</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>#!r6rs<BR>(library (aap)<BR> (export)<BR> (import (rnrs eval (6)) (rnrs base (6)) (rnrs io simple (6)))<BR> (write (eval (lambda (x) x) (environment '(rnrs base (6))))))</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>writes #<procedure>, which seems not to conform to R6RS, for a procedure is not a datum value.</FONT></DIV> <DIV><FONT face="Courier New" size=2>On the other hand with:</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>(eval '(define a 1) (environment '(rnrs))))</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>an error is reported: define: not allowed in an expression context in: (define a 1) which does conform to R6RS.</FONT></DIV> <DIV><FONT face="Courier New" size=2>BTW both R5RS and R6RS require two arguments for eval (the expression to be evaluated and an environment)</FONT></DIV> <DIV><FONT face="Courier New" size=2>Jos</FONT></DIV> <DIV><FONT face="Courier New" size=2></FONT> </DIV> <DIV><FONT face="Courier New" size=2>----- Original Message ----- </FONT> <DIV><FONT face="Courier New" size=2>From: "Cristian Baboi" <</FONT><A href="mailto:cristian.baboi@gmail.com"><FONT face="Courier New" size=2>cristian.baboi@gmail.com</FONT></A><FONT face="Courier New" size=2>></FONT></DIV> <DIV><FONT face="Courier New" size=2>To: <</FONT><A href="mailto:plt-scheme@list.cs.brown.edu"><FONT face="Courier New" size=2>plt-scheme@list.cs.brown.edu</FONT></A><FONT face="Courier New" size=2>></FONT></DIV> <DIV><FONT face="Courier New" size=2>Sent: Monday, July 14, 2008 8:00 AM</FONT></DIV> <DIV><FONT face="Courier New" size=2>Subject: [plt-scheme] Self evaluating "objects"</FONT></DIV></DIV> <DIV><FONT face="Courier New"><BR><FONT size=2></FONT></FONT></DIV><FONT face="Courier New" size=2>> Hello!<BR>> <BR>> I've tried the following expression in PLT 4.0.2 and Gambit-C 4.2.8 and  <BR>> got different answers:<BR>> <BR>> (eval (lambda (x) x))<BR>> <BR>> <BR>> PLT<BR>>> (eval (lambda (x) x))<BR>> #<procedure><BR>> <BR>> <BR>> Gambit-C<BR>>> (eval (lambda (x) x))<BR>> *** ERROR -- Ill-formed expression<BR>> #<procedure #4><BR>> 1><BR>> <BR>> I've browsed trough R5RS and R6RS and I was not able to figure out which  <BR>> behavior is the right one.<BR>> Is this implementation dependent or it is prescribed by some standard ?<BR>> _________________________________________________<BR>>  For list-related administrative tasks:<BR>>  </FONT><A href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme"><FONT face="Courier New" size=2>http://list.cs.brown.edu/mailman/listinfo/plt-scheme</FONT></A></BODY></HTML>