Guile and Scheme links
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There are many places you can go to on the Web to find out more regarding Guile and the Scheme programming language. We list a few of them here:
- A history and introduction to Scheme, with links to more sites, at the Wikipedia collaborative encyclopedia.
- R5RS is the official Scheme language definition and reference.
- A classic introduction to Scheme by Ken Dickey.
- Structure and Interpretation of Computer Programs by Abelson, Sussman, and Sussman (full text online).
- Introduction to Scheme and its Implementation (the complete book on-line) by Prof. Paul R. Wilson (Univ. of Texas).
- Teach Yourself Scheme is a nice tutorial-style introduction to Scheme programming.
- The MIT Scheme Home Page (where do you think Scheme was invented?)
- also check out the MIT Scheme Underground
- There is the comp.lang.scheme newsgroup, and its FAQ.
- The Internet Scheme Repository has a lot of code and documentation.
- schemers.org is another Scheme site and collection of resources.
Guile is a free implementation of Scheme, designed to be plugged in to other programs as a scripting language.
- The home site for the GNU Guile project.
- See parts IV and V of the Guile Reference Manual for additional Scheme functions and types defined within the Guile environment.
How to write a loop in Scheme
The most frequently asked question seems to be: how do I write a loop in Scheme? We give a few answers to that here, supposing that we want to vary a parameter x from a to b in steps of dx, and do something for each value of x.
The classic way, in Scheme, is to write a tail-recursive function:
(define (doit x x-max dx) (if (<= x x-max) (begin ...perform loop body with x... (doit (+ x dx) x-max dx)))) (doit a b dx) ; execute loop from a to b in steps of dx
There is also a do-loop construct in Scheme that you can use
(do ((x a (+ x dx))) ((> x b)) ...perform loop body with x...)
If you have a list of values of x that you want to loop over, then you can use
(map (lambda (x) ...do stuff with x...) list-of-x-values)
How to read in values from a text file in Scheme
A simple command to read a text file and store its values within a variable in Scheme is
read. As an example, suppose a file foo.dat contains the following text, including parentheses:
(1 3 12.2 14.5 16 18)
In Scheme, we would then use
(define port (open-input-file "foo.dat")) (define foo (read port)) (close-input-port port)
The variable foo would then be a list of numbers '(1 3 12.2 14.5 16 18).
libctl has a couple of built-in functions
interpolate (see the user reference) to construct lists of a regular sequence of values, which you can use in conjunction with
map as above:
(map (lambda (x) ...do stuff with x...) (arith-sequence x-min dx num-x))
(map (lambda (x) ...do stuff with x...) (interpolate num-x (list a b)))
Finally, if you have an entire libctl input file myfile.ctl that you want to loop, varying over some parameter x, you can do so by writing a loop on the Unix command-line. Using the bash shell, you could do:
for x in `seq a dx b`; do program x=$x myfile.ctl; done