131 lines
5.2 KiB
HTML
131 lines
5.2 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<HTML>
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<HEAD>
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<TITLE>Galapagos - Background</TITLE>
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<META NAME="Author" CONTENT="">
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<META NAME="GENERATOR" CONTENT="Mozilla/3.01Gold (Win95; I) [Netscape]">
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</HEAD>
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<BODY background=stone.jpg>
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<P>
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<CENTER>
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<A href="index.html"><IMG border=0 src=prev.gif ALT=" [PREV] "></A>
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<A href="extensions.html"><IMG border=0 src=next.gif ALT=" [PREV] "></A>
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<A href="index.html#toc"><IMG border=0 src=toc.gif ALT=" [PREV] "></A>
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</CENTER>
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<HR width=80% align=right color=blue>
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<P>
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<H2 ALIGN=CENTER><A NAME="top"></A><FONT SIZE=+4>Background</FONT></H2>
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<UL>
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<LI><A HREF="background.html#SCHEME">SCHEME</A></LI>
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<LI><A HREF="background.html#LOGO AND TURTLE">LOGO and Turtle Geometry</A></LI>
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<LI><A HREF="background.html#OBJECTIVES">Objectives</A></LI>
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<LI><A HREF="background.html#AVAILABILITY">Avaliability</A></LI>
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</UL>
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<H2>
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<HR WIDTH="100%"></H2>
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<H2><A NAME="SCHEME"></A>SCHEME</H2>
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<P>Scheme is a dialect of Lisp that stresses conceptual elegance and simplicity.
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It is specified in R4RS and IEEE standard P1178. Scheme is much smaller
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than Common Lisp; the specification is about 50 pages, compared to Common
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Lisp's 1300 page draft standard. (See the Lisp FAQ for details on standards
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for Common Lisp.) Advocates of Scheme often find it amusing that the entire
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Scheme standard is shorter than the index to Guy Steele's "Common
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Lisp: the Language, 2nd Edition".<BR>
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</P>
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<P>Scheme is often used in computer science curricula and programming language
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research, due to its ability to represent many programming abstractions
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with its simple primitives.<BR>
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</P>
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<P>There are a lot of traditional SCHEME interpreter available such as
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Chez, ELK 2.1, GAMBIT, MITScheme, scheme->C, Scheme48, T3.1, VSCM and
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Scm4e. Many free Scheme implementations (as well as SCM) are available
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from swiss-ftp.ai.mit.edu [18.43.0.246].<BR>
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</P>
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<P>Galapagos is built over the SCM interpreter version 4e4 written by Aubrey
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Jaffer <jaffer@ai.mit.edu>.<BR>
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<BR>
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<BR>
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</P>
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<H2><A NAME="LOGO AND TURTLE"></A>LOGO AND TURTLE GEOMETRY<BR>
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</H2>
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<P>LOGO is a programming language designed for use by learners, including
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children. It is a dialect of LISP which has a more natural syntax, using
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infix arithmetics and (almost) no parentheses. LOGO features a "turtle"
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which can be instructed to move across the screen and draw shapes. This
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became known as "Turtle Graphics" or "Turtle Geometry"
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- a geometry that describes paths "from within" rather than "from
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outside" or "from above." For example, "turn right"
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means turn right relative to whatever direction you were heading before;
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by contrast, "turn east" specifies an apparently absolute direction.
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A Logo user or program manipulates the graphical turtle by telling it to
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move forward or back some number of steps, or by telling it to turn left
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or right some number of degrees.<BR>
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</P>
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<P>Turtle geometry has two major advantages. One is that many paths are
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more simply described in relative than in absolute terms. For example,
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it's easy to indicate the absolute coordinates of the corners of a square
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with vertical and horizontal sides, but it's not so easy to find the corners
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of an inclined square. In turtle geometry the same commands (go <B>forward</B>,
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turn right 90 <B>degrees</B>, etc.) work for squares with any orientation.
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The second advantage is pedagogic rather than computational: turtle geometry
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is compatible with a learner's own experience of moving in the world -
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it's "body syntonic."<BR>
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</P>
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<P><A NAME="OBJECTIVES"></A><B><FONT SIZE=+2>OBJECTIVES</FONT></B><BR>
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</P>
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<P>The two major goals behind Galapagos were:<BR>
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</P>
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<P>First, we wanted to create an environment suitable for teaching programming,
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patterned after Logo's environment and its easy-to-understand, easy-to-use
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turtle geometry. We chose Scheme as the programming language because of
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its educational value, as noted before. We added Turtle Graphics because
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of its ability to visualize computations, and thus help understanding them
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better.<BR>
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</P>
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<P>Second, we wanted to add parallel programming. The importance of multiprocessor
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machines and of multithreading is becoming more apparent every day, and
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so is the need for tools to help understanding parallel programming paradigms.
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By extending Scheme to be multithreaded, we wanted to create such a tool.<BR>
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</P>
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<P><A NAME="AVAILABILITY"></A><B><FONT SIZE=+2>AVAILABILITY</FONT></B><BR>
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</P>
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<P>Galapagos was developed to run under Windows 95, and should work under
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Window NT as well. (It uses 32-bit specific code so Win32s is not enough
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to run Galapagos). Both binary and source are <A href="index.html#download">available</A> at the
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homepage:<BR>
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</P>
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<CENTER><P><TT>
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<A HREF="http://www.cs.bgu.ac.il/~elad/GALAPAGOS">http://www.cs.bgu.ac.il/~elad/GALAPAGOS</A>
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</TT>
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</P></CENTER>
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<P>
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<HR width=80% align=left color=blue>
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<CENTER>
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<A href="#top"><IMG border=0 src=back.gif ALT=" [TOP] "></A>
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<A href="index.html"><IMG border=0 src=prev.gif ALT=" [PREV] "></A>
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<A href="extensions.html"><IMG border=0 src=next.gif ALT=" [PREV] "></A>
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<A href="index.html#toc"><IMG border=0 src=toc.gif ALT=" [PREV] "></A>
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</CENTER>
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</BODY>
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</HTML>
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