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Gregg M. Townsend
Department of Computer Science
The University of Arizona
www.cs.arizona.edu/icon/uguide/relnotes.htm
Last updated July 10, 2022
This page summarizes changes in the official Arizona implementation of the Icon programming language:
Not all minor changes are listed here. For an exhaustive list, review the Git history at https://github.com/gtownsend/icon/commits/master.
The musl C library
can be used to build Icon by manually defining _MUSL
in CFLAGS when configuring or by using the new
linux_musl configuration.
A port to the Haiku
operating system is now included and can be selected by specifying
the haiku configuration.
For graphics programs, the environment variable DISPLAY
can now exceed 63 characters. This bug was exposed by the release of
Mac OS 10.10 (“Yosemite”).
Support for pre-1995 versions of the GNU C library was removed to adapt to internal changes in version 2.28 of 2018.
The core library files remain stable. Minor changes include:
procs/numbers gcd(i,j) now allows all argument values except i=j=0. procs/random choose(k,n) returns a set of k distinct integers in [1..n].
These features appeared in earlier releases of Icon but subsequent to publication of the Icon books.
An execution profile can be produced by setting the environment variable
ICONPROFILE at execution time to specify an output file.
For a separately built program, profiling must also be enabled during linking.
For each line of the program that is executed, the profiler reports the number of visits and also the number of timer ticks attributed to the line.
The report is ordered by memory layout, which is based on linkage order.
To arrange by filename, use the Unix sort utility
with keys –k3,3 –k4n.
To see the CPU hotspots, use sort –nr | head.
External code incorporated by loadfunc() can now create
and return to Icon code opaque values that can be stored and passed
on subsequent calls.
See External Values for more information.
Icon's X-windows interface no longer limits each window to 256 colors at one time. Median-cut quantization selects image colors when writing a GIF file.
An Icon source file can be made executable under Unix by prefixing it with a comment line
#!/usr/bin/env iconicon command,
which in another form allows a small Icon program to be embedded
within a shell script.
See the man page for details.
The traditional icont command
remains available when more flexibility is needed.
Under Unix, colons (:) may now separate directories in the
LPATH and IPATH environment variables as an
alternative to spaces.
The Icon translator and linker search these paths when looking for
$include and link files respectively.
The Icon program library is now searched automatically, but
LPATH and IPATH can still be set to control
the search order.
The effective path in each case is:
Other changes affect the configuration of Icon at installation time and the way executable Icon programs locate the interpreter. These changes, which are transparent to most users, are discussed in more detail on the File Organization page.
The files in a directory can be listed by opening the directory as a file.
Subsequent reads return the names of the files contained in the directory.
The names are returned in no particular order, and for Unix, the directories
"." and ".." are included.
The function read() recognizes
three kinds of line terminators when reading a file
opened in translated mode:
Windows (CR+LF), Macintosh (CR), or Unix (LF).
Consequently, text files created on one platform can be
read by an Icon program running on a different platform.
Icon deals strictly in 8-bit characters and expects a superset of ASCII such as ISO 8859-1 (“Latin 1”). It does not translate UTF-8 escape sequences and does not support Unicode.
Large integers cannot be used with i to j,
with seq(), or with integer-valued keywords.
Large-integer literals are constructed at run-time, so such literals are best kept outside of loops.
Conversion of a large integer to a string is quadratic in the length of the integer. Conversion of a very large integer may take a long time.
An "evaluation stack overflow" can occur when a procedure is called
with a huge number (thousands or more) of arguments.
The capacity can be increased by setting the environment variable
MSTKSIZE or COEXPSIZE, as appropriate.
Stack overflow checking uses a heuristic that is not always effective. Stack overflow in a co-expression is especially likely to escape detection and cause a mysterious program malfunction.
Pathologically nested structures can provoke a memory or segmentation
fault during garbage collection by reaching the stack limit.
The stack limit can be raised by the
limit or ulimit shell command.
If an expression such as x := create expr
is used in a loop, and x is not a global variable,
uncollectable co-expressions accumulate with each iteration.
This problem can be circumvented by making x
a global variable or by assigning a value to x
before the create operation, as in
x := &null
x := create expr
Integer overflow on exponentiation may not be detected during execution. Such overflow may occur during type conversion.
When a comparison operation must convert its right operand for
type compatibility, the converted value is returned on success.
For example, the expression
2.5 < 3 returns the value 3.0.
Icon graphics facilities utilize only server-side fonts (those listed
by xlsfonts) and not the more modern client-side fonts.
Now that graphics memory is cheap, very few platforms require or support mutable colors. Icon code for mutable colors is still present but untested.
Windows are not always refreshed properly while a program is blocked awaiting standard input.
Depending on the window manager, values set and read back from the
pos, posx, and posy attributes
may be slightly inconsistent.
The $DISPLAY bug (noted above as a minor fix)
exposed problems when a program uses multiple displays.
CopyArea() calls are not properly clipped,
and the management of colors is suspect.
See the documentation guide for an overview of the available Icon documentation.
For installation instructions, see Installing Binaries or Building from Source as appropriate.
Steve Wampler suggested the gcd liberalization.
Sean Jensen fixed an ancient bug in the lexer.
Cheyenne Wills provided the GNU C library fix
and the musl adaptation.
Arthur Eschenlauer provided the linux_musl configuration.
The GitHub user “turboencabulator” noted and fixed
several questionable uses of signed values.
He and Cheyenne Wills both, independently, isolated a nasty bug
in the string conversion of MinLong.
Jason Martin supplied the Haiku port.