244 lines
11 KiB
Plaintext
244 lines
11 KiB
Plaintext
--*- Mode: Indented-text; -*-
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Scheme 48: list of bugs and things to do.
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Last update by RAK on 28 April 1998.
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Run-time system bugs:
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Shadowing can fail sometimes for macro-referenced variables. E.g.
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the following sequence will lose if entered interactively as
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three separate forms:
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(define (foo x) `(a ,x))
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(define cons list)
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(foo 1) => (a (1 ()))
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Programming environment:
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Fuller on-line documentation.
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Error recovery. Can do better than ,proceed. LOAD should set up
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restart continuations.
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Types in scheme-interface (and elsewhere) aren't as tight as they
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could be.
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LET continuation "pessimization" to retain the environment longer.
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Have the disassembler display local variable names.
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This ought to be recoverable, but isn't always:
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> (let loop ((x '())) (loop (cons 3 x)))
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not enough room in heap for stack
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The get-cont-from-heap instruction should have an exception
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discloser that indicates the actual error (returning a
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non-fixnum from application top level).
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Separate compilation (compile a module, writing object code to a
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file). (Rudiments in misc/separate.scm)
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Semicolon comments don't quite work after commands (extra newline
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required).
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Command (and procedure) to change current directory.
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Some procedure in EXEC to take the place of ## in moving values from
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one package to another: (transport <from-package> <exp> <to-package>
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[<id>]), and/or have eval etc. commands return the value
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Batch mode should write error messages to (error-output).
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Performance:
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Generational GC.
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More compact representation for debugging data?
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Leaf procedure compilation (RK's rts/no-leaf-env.scm): if no
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continuations or lambdas, skip the make-env and access locals
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using stack-ref. Expected to gain about 6% in speed.
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Optimize loops somehow (maybe using call-template opcode and/or
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opportunistic compilation).
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The CAML light implementation has good documentation and patches
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for optimizing the interpreter's switch (*pc++); perhaps we
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could lift some of it. (Range check isn't necessary.)
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Floating point support in VM.
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Bignum support in VM: use MIT Scheme bignums or GNU Multiple
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Precision Arithmetic Library (Torbjorn Granlund <tege@sics.se>).
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Faster bignum printer (e.g. the one Richard wrote - but it would be
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nice if it were an option tied to bignums, not built in to the
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initial image).
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Ratnum multiplication and division might be made more efficient by
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taking cross-GCD's.
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Native code compiler...
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Big Scheme bugs / features:
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It would be nice to be able to simulate control-C interrupts on
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a port other than the initial input port - e.g., on a socket.
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This would require creating a new thread to act as a front end.
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The new thread would read characters eagerly, buffering
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everything except control-C's for the thread that is doing the
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real work, and converting control-C's into interrupts.
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How about deleting entries from tables?
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RPC.
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Add call/gcc (invokes the Gnu C compiler).
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Module system bugs:
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,untrace should undefine as well if the variable wasn't bound
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before.
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Compound signatures don't get updated when a component signature
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changes. They contain a list of signatures with no reinitialization
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thunk a la structures and packages.
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Module system features:
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Check for name conflicts between opened structures.
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Implement interface subtraction as a way of dealing with such
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conflicts: (WITHOUT (<name> ...) <interface>)
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Check for cycles in structure inheritance.
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An ,access command, similar to ,open.
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Deal with package system state better (for linker). Maybe each
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package should point to a data structure containing
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*location-uid*, location-name-table, *package-uid*,
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package-name-table, and perhaps the compiler-state as well (see
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segment.scm).
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VM:
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Heaps that can grow larger.
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Add a test to configure.in that can determine whether ld -A works.
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If both it and dlopen() work, then both kinds of dynamic loading
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should be made available.
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Merge in Olin's changes and extensions (command line processing,
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the #! syntax for scripts, external function call, etc.).
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Interrupt while writing out image causes an exit. [Fixed?]
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A jump-back instruction? Might be easier to use than call-template.
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Scrutinize all VM fatal errors to see if any can be recovered
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from. E.g. "out of ports" shouldn't cause a VM halt, it should
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just cause open-port to return #f or an error code. [Fixed?]
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Get VM interp.scm-without-gc.scm working again.
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Documentation:
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Describe (optimize auto-integrate).
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How to use the static linker.
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How initial.image and scheme48.image get built, really.
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Techniques for debugging the runtime system (debug/for-debugging.scm).
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Cleanup:
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VM:
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Rename "unassigned" to "uninitialized"? Or phase it out entirely.
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In unix.c, use getrusage(), when available, to get run time.
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Run-time / features / development environment:
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A DIVIDE procedure (maybe an instruction as well) that returns two
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values.
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Figure out how to merge the two type systems (META-METHODS and
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META-TYPES). The generic function system could make use of the
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SUBTYPE? and INTERSECT? predicates.
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Correct floating point, esp. reading and printing. And
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(= 1/3 (/ 1. 3.)) returns #t, but ought to return #f.
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Parameterize over file name syntax somehow. Currently
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big/filename.scm assumes Unix (cf. DIRECTORY-COMPONENT-SEPARATOR,
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FILE-NAME-PREFERRED-CASE). Perhaps there should be VM support for
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this.
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Make sure that the disassembler and assembler are inverses of one
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another.
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Disassembler should generate S-expression first, and then print
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it independently.
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Combine conditions, signals, and handle into a single structure?
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Figure out a better way to implement ##.
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Be consistent about "filename" versus "file-name".
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Compiler / linker / module system:
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The "reflective tower" isn't really a reflective tower, it's a
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syntactic tower. Rename it.
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The scanner (file loader) should operate on streams, not lists.
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This would result in more uniform and flexible internal
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protocols for reading files, scanning for DEFINEs, compiling,
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and running - passes could be interleaved or separated easily.
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Flush link/data.scm. Linker should instead open the VM module
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that includes vm/data.scm.
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Flush (optimize ...) clause in DEFINE-STRUCTURE in favor of
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optimizer argument to SCAN-STRUCTURES.
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Vector patterns and templates ought to be supported in
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SYNTAX-RULES.
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The DEFINE-INTERFACE forms should contain types for every exported
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variable; the code in cprim.scm (and recon.scm?) shouldn't have
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to worry about setting up types.
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Add ENVIRONMENT-DEFINED? ?
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Make USUAL-TRANSFORM return a transform?
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Add enough to the node signature to make it usable on its own?
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make-c-header-file should put definitions for the interrupt
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enumeration into scheme48.h, and unix.c et al should use them.
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Flatloading and loading are very different operations, so FLATLOAD
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shouldn't do SET-PACKAGE-LOADED?!; instead it should maintain its
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own list of flatloaded packages (in a global variable, say).
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Etc:
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Start using a source control system (like rcs).
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There ought to be a sanity check to ensure that the size of the
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area as computed by static.scm agrees with the size as computed
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by C's sizeof() operator.
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What should (syntax-rules (x) ((foo ?body) (let ((x 1)) ?body))) do?
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To: jar@cs.cornell.edu
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Subject: Not a bug this time. :-)
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Date: Tue, 22 Feb 94 19:13:37 -0500
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From: Paul Stodghill <stodghil@cs.cornell.edu>
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The result of ,expand can be confusing. In particular, it doesn't
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distinguish between different identifiers that have the same name.
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For instance, in the example below, it would be more useful if the result
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of the ,expand was something like,
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'((lambda (.x.1) (set! x (- .x.1))) x)
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Welcome to Scheme 48 0.31 (made by jar on Sun Feb 13 18:33:57 EST 1994).
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Copyright (c) 1993, 1994 by Richard Kelsey and Jonathan Rees.
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Please report bugs to scheme-48-bugs@altdorf.ai.mit.edu.
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Type ,? (comma question-mark) for help.
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> (define-syntax foo
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(syntax-rules ()
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((foo var) ((lambda (x) (set! var (- x))) var))))
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> (define x 1)
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> ,expand (foo x)
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'((lambda (x) (set! x (- x))) x)
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>
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Date: Mon, 14 Jun 93 18:33:30 HKT
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From: shivers@csd.hku.hk
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To: kelsey@flora.ccs.neu.edu
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Cc: jar@cs.cornell.edu
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Subject: Scheme 48
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...
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All true. My major motivation was portability. I also found the module system
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to be a big win. Other things that influenced me were (1) elegance and
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modularity -- I felt I could comprehend and mung the system as needed (2)
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reasonable efficiency and small size and (3) real, full R4RS+ support (most
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small systems do it partly).
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Actually, I wouldn't say the programming environment is particularly
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exceptional, unless you count the module system.
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A small thing lacking in other Schemes that really reduced my debug times: the
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loader would complain about undefined free var refs in my code. This
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frequently picked out variable spelling errors, inconsistent name linkages,
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and forgotten procedure defs. Not a big thing, but really effective.
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Another win was simply having the implementors around for detailed
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explanations and support.
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Problems I had with S48:
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- Inability to mess with the VM, as it is written in a language that can
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be compiled by only 1 person in the world.
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- The foreign-function support was quite limited, and the foreign-data support
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was basically non-existent. Exporting gc'd data to C, gc'ing data allocated
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in C, hooks into the GC, importing C data into Scheme -- no support. Elk
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handles this better, as that is critical to the type of applications at
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which elk is targeted.
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I fixed some of this myself -- helped by your general, portable low-level ff
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interface, which was well-designed in terms of those goals -- but I couldn't
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do much about foreign-data support.
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- No support currently for linking static heap data into a text-pages
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area to reduce gc copying and shrink the dynamic heap.
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- The module system was frequently frustrating. The non-uniform , command
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language, bugs, the restrictions of living with a module system,
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being blocked from accessing primitives whose bindings had been
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gc'd away at link time, and awkwardnesses in the user interface really
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slowed me down.
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The module system was also a great help; these are simply the problems
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of life with an experimental system, as opposed to a polished final
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product.
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[But] all in all, S48 was the best choice I could have made.
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