2026-07-20: Fuzion July Update

The work on Fuzion's version of fearless concurrency continued by adding more consistency to the use of mutate effects as the base mechanism of synchronization and by laying the foundations of what will becomre Fuzion's realtime APIs.

• General

  • Fuzion release 0.097 (#7246, #7248)

• Fuzion language

  • Use $(expr) instead of {expr} to embed expression into a string #6670 (#7107). This results in more consistent syntax and avoids the required escaping for { and }:

      say "x is $x, x² is $(x**2)"
              

    must now be used instead of

      say "x is $x, x² is {x**2}"     # *** no longer supported syntax
              

    Note that prefix $ is a shorthand for as_string, so outside of a string $(x**2) would create the String literal representation of (x**2) as well, making the syntax somewhat consistent.

• Base library

  • Changes related to Concurrency

    • concurrent use of mutate or blocking_mutate now produce consistent errors (precondition failures) for accesses that require exclusivity that are not exclusive. Fix #7166, error handling for concurrent use of mutate (#7173).

    • in exclusive, check wakeup-conditions while still holding mutex (#7174)

    • cleanup and additional functions for Channel (#7189) to make their use more similar to golang's channels.

    • Sending_Channel.infix <- now panics if closed even in precondition. (#7196)

    • blocking_mutate no recursive checking for wait conditions, fix #7217 (#7219)

    • provide wait/signal/broadcast without error result (#7235)

    • make close on mutable variable require is_exclusive (#7244)

    • in blocking_mutate, add missing wakeup in wait (#7265)

    • add choice-type for scheduling policy (#7160)

    • added a very basic API for realtime.tasks (#7193)

    • add atomic.update (#7176) so you can do, e.g.,

        i := concur.atomic i32 .new 12
        old,new := i.update i32->i32 **2
        say "$old $new"'
                

      which will print 12 144.

  • New library features

    • added codepoint.as_u8, hid String.type.minus_char etc. (#7247, #7255).

      It is now possible to do, e.g. say "-".as_u8 to get a codepoint value that fits into an u8, i.e., codepoints from the unicode pages C0 Controls and Basic Latin and C1 Controls and Latin-1 Supplement.

    • added features to obtain Fuzion version (#7161): fuzion.runtime.version returns the Fuzion version string.

    • Add method as_string_decimals to convert a float to a string with a custom number of decimals (#7152)

  • Changed library features

    • add precondition to Ring_Buffer to ensure non negative size (#7186)

    • add wrapper type uid to be used by unique_id effect (#7157)

    • call *_write for socket, file or pipe until error or all bytes written (#7197) to avoid losing data on partial write.

    • change array length type to i64 and use type parameter for index access (#7200)

    • do not silently ignore error results in debug mode (#7203)

    • fix concatenating known infinite Sequence to Finger_Tree (#7137)

    • improve error message in os.process (#7134, #7155)

    • io.write minor change in argument names (#7141)

    • make Nullary inherit from auto_unwrap (#7251)

    • rename yak as yap (#7165)

    • support calling path.as_absolute on already-absolute paths (#7191)

    • switch, add more generic or_panic (#7201)

    • time/frequency: fully qualify inheritance from time.Period (#7181)

  • Removed library features

    • Remove shorthands to access effects (#7162).

      This makes code using effects more explicit: One has to write, e.g.,

        io.Err.env.println "some text"
                    

      instead of hiding the effect access via

        io.err.println "some text"
                    

• Parser

  • fix bug where lexer and string lexer went out of sync (#7123)

  • use sourceRange for position of an if for nicer error messages (#7144)

• Front end

  • Better error message when attempting to call a choice feature: add special case to calledFeatureNotFound when trying to call a choice (#7170)

  • change logic in AbstractCall.adjustResultType to fix precondition failure from issue #7108 (#7164)

  • further simplify result type logic in Call/AbstractCall (#7214)

  • handDownListToType, small refactoring (#7240)

  • minor code refactoring, pulled out logic for effectiveResultType in own method (#7212)

  • refactor applyTypePars_ a bit (#7260)

  • refine code constraintAssignableFrom (#7159)

  • suppress followup error for result type **error** in native feat (#7150)

  • trying to simplify adjustResultType and friends (#7213)

  • addDeclaredOrInherited, fix logic for repeated inheritance of redefined features (#7230)

  • better type inference for num literals in lambda results (#7224)

  • change outer in inherits call features visitation (#7210)

  • confusing error: “expected formal type: ‘T’ actual type found : ‘T’” (#7136)

  • enhance errors for loop termination condition resulting in non boolean (#7253)

  • fix missing source position in “Illegal this-type” error message (#7254)

  • improve error message when loop is assigned to result field (#7143)

  • make fum files building reproducible (#7168)

  • raise error if outer is called on this-type (#7245)

  • rename adjustResultType methods (#7269)

  • support auto_unwrap of match subjects and if conditions (#7228)

  • suppress visibility reporting for call to outer ref (#7172)

  • fix generics of normaltype containing an unresolved type (#7192)

  • rename internal THIS#TYPE as RELAY#TYPE (#7268)

  • rename, isGenericArgument -> isParametricType, etc. (#7267)

• Middle end

  • return NO_CLAZZ for assigns where field result clazz is of unit type (#7236)

  • try fix outer normalization (#6969)

• Runtime System

  • jvm: more readable stack trace, fix most of #7169 (#7179)

  • posix, remove set_last_error function and last_error field (#7258)

  • make fzE_file_read handle EINTR (#7154)

• Backends

  • C backend

    • be/c: posix, do not heap allocate pthread_t (#7206)

• Windows

  • update wolfssl library name (#7272)

• macOS

  • fix _unlocked versions not present on macOS (#7237)

• Tests

  • fix test_duration sort order (#7242)

  • add regression test for already fixed issues (#7238, #7229)

  • check_example, replace clazzIds by XXX (#7139)

  • remove time.nano.env.sleep with arbitrary values (#7243)

  • update lsp test (#7133)

• Build Infrastructure

  • dockerfile: upgrade to ubuntu 26 (#7148)

• Documentation

  • readme: add instructions on how to build the language server (#7239)

  • title change wording from type argument to type parameter as according to ref manual (#7234)

• Fuzion Webserver

  • cleanup: call effect instance features via env (#425)

  • incremental update of running examples (#422)

  • replace sieve cache by lock free map in global.env.sessions. (#424)

  • runner: output both stdout and stderr regardless of exit_code (#416)

  • specify type parameter explicitly to avoid error (#418)

• Feeze

  • Started porting of the recorder part for feeze to Fuzion (commit #a17a917).

Cheers,

--The Fuzion Team.