Version history

This document details the changes made to Mars since its first release. This is a fairly high-level document, describing only the visible changes. For details on the individual bugs fixed, see the bugs targeted to each release in the trunk series. For a complete history of changes to Mars, see the commit log.

Version 0.3.1

Released Thursday, 27 Oct 2011

This version focuses almost exclusively on redesigning the Mars internal representation so that it is easier to implement in low-level back-ends such as LLVM. While there are almost no publicly-visible changes, the instruction set architecture is drastically different than in previous versions. The code generator has to work much harder to generate lower-level code, but this pays off in that the many different back-ends have a much easier job to do.

Bug fixes

  • Case-bound variables now conform to SSA, preventing internal errors for some programs. (LP: #578068)
  • Fixed temporary names being reused within a single-case switch. (LP: #682536)
  • Fixed interactive mode not catching errors raised by evaluating CGCs. (LP: #697929)
  • Fixed interactive mode remembering the value of every temporary variable in the history of the session. (LP: #871725)
  • Fixed mars.exec_main_func; now puts the result in the localtable. (LP: #600467)
  • Internal software errors now go to stderr, not stdout. (LP: #690053)
  • When printing the environment, fixed internally representing constructor names with gvname, which they aren’t supposed to be represented as. (LP: #700862)
  • Fixed the built-in show type (the variable a was not rigid). (LP: #708486)
  • The test framework now reports test cases that crash and those that don’t end properly. (LP: #576385; #690054)
  • Readline completion no longer shows internal (synthetic) functions. (LP: #702205)
  • The “:e” display no longer shows subscripted variables. (LP: #710450)
  • Fixed the ordering of blocks in the Mars IR code. It now reasonably well follows the order of the original source code. (LP: #412367)

Internal changes

  • The show and eq functions are now implemented non-primitively using type dictionaries (see Type dictionaries). This means back-ends do not need to supply an implementation for these type-specific functions. (LP: #710495)
  • Changed the semantics of the field access instructions so they are much lower level. The code generator now generates field access functions in Mars IR to non-primitively perform the high-level actions. The instructions implemented by the back-end now perform very simple tasks. (LP: #690017)
  • There is now an instruction for directly calling a constructor, rather than having to load it into a local function first. (LP: #766796)
  • Major change to Mars IR: global variables are no longer accessible as variable names (only local variables). Rather, we provide special instructions to call and load the value of global variables. (LP: #699721)
  • Mars IR can no longer partially apply functions. Replaced this feature by introducing “closure templates” which are much easier to implement on low-level back-ends. The code generator must now generate a closure template for each partial application, which explicitly accepts a certain number of parameters in its closure. (LP: #744760)
  • Removed instructions for loading int literals and constructor symbols; instead, int literals and constructor symbols are considered to be “atoms” along with variable names, and atoms can now be referenced by most instructions that used to refer only to variable names. (LP: #440429)
  • Renamed the internal function ir.varname_to_string_noescape to simply ir.varname_string. (LP: #690456)

Miscellaneous

Version 0.3.0

Released Friday, 25 Jun 2010

Core language changes

  • Pattern bindings in case statements are now like any other assignment – scoped to the entire function and in the same namespace as all the other locals. Patterns no longer create a new scope, and the variables they create no longer shadow existing locals. It is now a type error if a local variable has the same name but different type as a pattern variable (backwards incompatible). (LP: #513638)
  • It is now a compiler error if a switch statement does not cover all possible constructors of the type it switches over, preventing the possibility of runtime pattern match failure errors (backwards incompatible). (LP: #408411)
  • Variables no longer require declaration. Any variable assigned in a function is now implicitly a local variable. It is no longer an error to assign to a global variable or an undefined variable (this just creates a new local variable). (LP: #483082)
  • The field reference and replace expressions and the field update statement now work (previously they displayed “not implemented” errors). It is now possible to access and update individual fields of an object by name, without having to use a switch. (LP: #439171)
  • The field replace statement is now an expression; its result is the updated object. It previously didn’t make much sense because the statement performed an implicit assignment of its source variable. (LP: #408301)
  • The field update operator changed from “=” to “=!”, reflecting its impure nature. (LP: #595782)
  • It is now an error to have two fields of the same name in a given constructor. (LP: #513585)
  • It is now an error to have two variables of the same name in a given pattern. (LP: #509939)
  • Reading the value of (and therefore executing the body of) a computable global constant now caches the result so subsequent reads do not re-execute the body. Previously CGCs would be re-executed on each read. (LP: #491697)

Library changes

  • The built-in is function has been moved to the impure module. (LP: #582634)
  • The is function now works on objects of user-defined types (previously always returned 0). (LP: #585724)
  • Added prelude function ref which gets the element of a list with a particular index. (LP: #582635)

Bug fixes

  • Paul Bone: Fixed error compiling Mars on some systems, due to Readline code. (LP: #552168)
  • Critical type safety problem – if a declared local variable and pattern binding have different types, after the switch, the variable name has the declared type, but the value bound by the case (of the wrong type). Fixed by giving pattern bindings the full function scope, forcing them to have the same type as any declared variable. (LP: #513638)
  • Internal error “Phi missing predecessor in CFG” for programs with complex nested switches. (LP: #567082)
  • Internal error “Field reference to something not an ADT” for case statements with a nested pattern with two fields. (LP: #576375)
  • Type error for cases with int literals on polymorphic types. (LP: #509457)
  • Internal error for string literals with '\0. (LP: #534159)
  • Internal error calling error or get_env with '\0 in string. (LP: #534161)
  • Library function encodeURIComponent gives garbage output on strings with non-byte characters. (LP: #585703)
  • Now correctly sets the exit status of Mars to the result of main – rounds to a machine-size int with wraparound rather than using mod. (LP: #552413)
  • The show function now correctly includes empty parens for terms built from nullary constructors. (LP: #587787)

Test suite and internal changes

  • Replaced “dummy term binding” technique with explicit rigid type variables (as now described in documentation for type unification). (LP: #488595)
  • The control-flow graph (CFG) representation now includes full type information. (LP: #574108)
  • The t_switch instruction no longer includes fully-recursive patterns, but a limited format which matches only a single tag. Switch statements are now factored into this much lower-level construct which is easier to compile into machine code. (LP: #408411)
  • The interactive environment now uses SSA variable names, so variables which are re-assigned are no longer physically clobbered in the environment; they are assigned with a new qualified name. This makes the semantics of interactive consistent with the rest of the language and fixes issues with certain backends or analyses. (LP: #580487)
  • Fixed test suite silently treating invalid “outcome” values as “fail”. (LP: #574141)
  • No longer generates code for statements which are inaccessible because they are preceded by a return statement. This prevents malformed code generation. (LP: #517403)
  • Fixed parser not allocating a type to subexpressions of expressions which already have a type annotation. (LP: #578082)
  • Interactive mode executes type-annotated versions of statements. (LP: #578084)
  • Test suite is now orders of magnitude faster to run (fixed re-compilation for every case, causing N^2 behaviour). (LP: #589000)
  • Interpreter interface is now abstracted so it is possible to plug in different interpreter backends. (LP: #550708)
  • In the test framework, expecting a compile error now causes all of the runtime tests to be expected to be skipped, so they don’t raise large errors when they are. (LP: #596734)
  • Terminator instructions now hold a context object. (LP: #408291)
  • Function signatures no longer have an “argmode”. This was part of some uniqueness information analysis which was abandoned for a different representation, and has since been unused and completely obsolete. (LP: #550739)

Miscellaneous

  • All library functions are now documented. (LP: #486958)
  • The documentation is now syntax-highlighted for all Mars code. (LP: #576776)
  • If a bug in Mars causes an internal error, it will be displayed much more neatly, with a link to the “file bug” page on the bug tracker. (LP: #534165)
  • The test framework no longer generates .py files with Mars assembly (a bug dating back to when we actually generated Python output). (LP: #521992)
  • The src directory now includes a Makefile, so Mars can be compiled with a simple make. (LP: #522477)
  • The Mars Vim script (misc/mars.vim) has an updated list of built-in names. (LP: #539368)

Version 0.2.1

Released Friday, 27 Nov 2009

Core language changes

  • Rather than searching the current directory for imports, searches the directory the initial module is located in. This makes multi-module programs possible, without having to run them from the current directory or add them to MARSPATH.
  • No longer searches for the prelude in the current directory.
  • Mars now allows source files with DOS/Windows newlines.

Library changes

Bug fixes

  • Fixed unbounded stack growth during interpretation. Programs can now run for arbitrary lengths of time.
  • Cyclic imports now work properly (previously failed if the top-level module was involved in an import cycle).
  • String literals now have type Array(Int), not Array(a) (minor fix).
  • Interactive: Fixed interactively-assigned variables sometimes losing part of their type, causing them to be usable where they shouldn’t, and also strange type errors.
  • Interactive: Fixed exception associated with assigning an error expression to a variable, and then reading the variable’s value.
  • __impure_array_extend pre-grows the array to the full size, to avoid multiple regrows.
  • Fixed syntax error messages with special or non-ASCII characters.
  • Now fails correctly if given a directory name on the command line.

Miscellaneous

  • Interactive: Added readline support (proper command-line editing and completion). Mars now depends upon the GNU Readline library.

Version 0.2.0

Released Saturday, 03 Oct 2009

Library changes

  • Renamed impure primitives array_set, array_append and array_extend to __impure_array_set, etc; these are now deprecated. Added new module impure which provides the original names for these functions.
  • prelude – Added constant eof with a value of -1.

Bug fixes

  • Fixed software exceptions on user array bounds errors (now displays proper Mars errors).

Test suite and internal changes

  • Fixed testing framework (was broken on compilation testing).
  • Test cases – More tests for runtime errors.
  • Internal representation – Now uses an instruction-based representation rather than statement/expression-based. This is visible in the “asm” backend output.

Miscellaneous

  • marsc - Removed “python” backend. Added “asm” backend.
  • Documentation – Finished Introduction to Mars section. Added more language features, and removed references to the language Venus.
  • Documentation – Renamed “functions” to “procedures” when referring to a function as defined in source code, and renamed “parameter-less function” to “computable global constant”.
  • Samples – Added sample input to samples/bfs.mar.

Version 0.1.0

Released Wednesday, 07 Jan 2009

  • First release of Mars. Includes complete interpreter/compiler and documentation (though buggy and missing some features).