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a68g - Man Page


a68g [--apropos | --help | --info [string]] [--assertions | --no-assertions] [--backtrace | --no-backtrace] [--brackets] [--check | --no-run] [--compile | --no-compile] [--clock] [--debug | --monitor] [--echo string] [--execute unit | -x unit] [--exit | --] [--extensive] [-f | --file string] [--frame number] [--handles number] [--heap number] [--listing] [--moids] [-O | -O0 | -O1 | -O2 | -O3] [--object | --no-object] [--overhead number] [--optimise | --no-optimise] [--pedantic] [--portcheck | --no-portcheck] [--pragmats | --no-pragmats] [--precision number] [--prelude-listing] [--pretty-print] [--print unit | -p unit] [--quiet] [--quote-stropping] [--reductions] [--rerun] [--run] [--script string] [--source | --no-source] [--stack number] [--statistics] [--strict] [--terminal] [--time-limit number] [--trace | --no-trace] [--tree | --no-tree] [--unused] [--upper-stropping] [--verbose] [--version] [--warnings | --no-warnings] [--xref | --no-xref] filename


Algol 68 Genie (Algol68G) is an Algol 68 compiler-interpreter. It can be used for executing Algol 68 programs or scripts. Algol 68 is a rather lean orthogonal general-purpose language that is a beautiful means for denoting algorithms. Algol 68 was designed as a general-purpose programming language by IFIP Working Group 2.1 (Algorithmic Languages and Calculi) that has continuing responsibility for Algol 60 and Algol 68.

Algol 68 Genie and its documentation can be obtained from



Options are passed to a68g either from the file .a68g.rc in the working directory, the environment variable A68G_OPTIONS, the command-line or from pragmats.

Option precedence is as follows: pragmat options supersede command-line options, command-line options supersede options in environment variable A68G_OPTIONS, A68G_OPTIONS supersedes options in .a68g.rc.

Listing options, tracing options and -pragmat, -nopragmat, take their effect when they are encountered in a left-to-right pass of the program text, and can thus be used, for example, to generate a cross reference for a particular part of the program.

Where numeric arguments are required, suffices k, M or G are allowed for multiplication with 2 ** 10, 2 ** 20 or 2 ** 30 respectively.

--apropos | --help | --info [string]

Print info on options if string is omitted, or print info on string otherwise.

--assertions | --no-assertions

Control elaboration of assertions.

--backtrace | --no-backtrace

Control whether a stack backtrace is done in case a runtime-error occurs.


Consider [ .. ] and { .. } as being equivalent to ( .. ). Traditional Algol 68 syntax allows ( .. ) to replace [ .. ] in bounds and slices.

--check | --no-run

Check syntax only, the interpreter does not start.


Report execution time excluding time needed for compilation.

--compile | --no-compile

Switch compilation of units on or off. Compilation omits many of the runtime checks offered by the interpreter proper. The program is not executed and a shell script is generated combining source code and its shared library. This shell script can be used as a pseudo-executable.

--debug | --monitor

Start in the monitor. Invoke the monitor in case a runtime-error occurs; the program will pause in the monitor on the line that contains the error.

--echo string

Echo string to standout.

--execute unit | --x unit

Execute the Algol 68 unit. In this way one-liners can be executed from the command line.

--exit | --

Ignore further options.


Generate an extensive listing.

-f | --file string

Accept string as filename in case it conflicts with shell syntax.

--frame number

Set the frame stack size to number bytes.

--handles number

Set the handle space size to number bytes.

--heap number

Set the heap size to number bytes.


Generate a concise listing.


Generate an overview of modes in the listing file.

--object | --no-object

Control the listing of C code in the listing file.

--optimise | --no-optimise

Switch compilation of units on or off. Compilation omits many of the runtime checks offered by the interpreter proper. This option is equivalent to -O2.

-O | -O0 | -O1 | -O2 | -O3

Switch compilation of units on and pass the option to the back-end C compiler to set the optimiser level.

--overhead number

Set overhead for stack checking.


Equivalent to --warnings --portcheck

--portcheck | --no-portcheck

Enable or disable portability warning messages.

--pragmats | --no-pragmats

Control elaboration of pragmats.

--precision number

Set the precision for LONG LONG modes to number significant digits.


Generate a listing of preludes.


Pretty-print the source file.

--print unit | --p unit

Print the value yielded by the Algol 68 unit. In this way one-liners can be executed from the command line.


Suppress all warning messages.


Use quote stropping.


Print reductions made by the parser.


Use compiled code of a previous run.


Override the --no-run option.

--script string

Takes string as source file name and skips further option processing so these can be handled by the script.

--source | --no-source

Control the listing of source lines in the listing file.

--stack number

Set the stack size to number bytes.


Generate statistics in the listing file.


Ignores extensions to Algol 68 syntax.

--time-limit number

Interrupt the interpreter after number seconds, generating a time limit exceeded error.

--trace | --no-trace

Control tracing of the running program.

--tree | --no-tree

Control listing of the syntax tree in the listing file.


Generate an overview of unused tags in the listing file.


Use upper stropping, which is the default stropping regime.


Use verbose mode.


Print the version of the running image of a68g.

--warnings | --no-warnings

Enable warning messages or suppress suppressible warning messages.

--xref | --no-xref

Control generation of a cross-reference in the listing file.


Author of Algol 68 Genie is Marcel van der Veer <algol68g@xs4all.nl>.


February 21, 2024