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diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 index 00000000..bab499f5 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,149 @@ +Changelog +========= + +Sail 0.8 +-------- + +###### More flexible type synonym syntax + +Can now define type synonyms for kinds other than type. For example: +``` +type xlen : Int = 64 +type xlenbits = bits(xlen) +``` +the syntax is +``` +type <name> : <kind> = <value> +``` +for synonyms with no arguments and +``` +type <name>(<arguments>)[, <constraint>] -> <kind> = <value> +``` +for synonyms that take arguments. Valid kinds are `Int`, `Bool`, `Ord`, and +`Type`. `: Type` or `-> Type` can be omitted. + +This can be used to define constraint synonyms, e.g. +``` +type is_register_index('n : Int) = 0 <= 'n <= 31 +val my_function : forall 'n, is_register_index('n). int('n) -> ... +``` +Type synonyms with constraints and multiple arguments can be declared as e.g. +``` +type my_type('n: Int, 'm: Int), 'n > 'm > 0 = vector('n, dec, bits('m)) +``` + +The previous syntax for numeric constants (which was never fully implemented) of +``` +constant x = <value> +``` +is no longer supported. + +###### Emacs mode improvements + +Can now use `C-c C-s` in Emacs to start a Sail interactive +sub-process, assuming `sail` is available in `$PATH`. Using `C-c C-l` +or simply saving a changed Sail file will cause it to be checked. Type +errors will be highlighted within the Emacs buffer, and can be jumped +to using `C-c C-x`, much like Merlin for OCaml. `C-c C-c` will display +the type of the expression under the cursor for a checked Sail +file. This particular is slightly experimental and won't always +display the most precise type, although Emacs will bold the region +that sail thinks is under the cursor to make this clear. The +interactive Sail session can be ended using `C-c C-q`. + +To support multiple file ISA specifications, a JSON file called +sail.json can be placed in the same directory as the .sail files. It +specifies the dependency order for the .sail files and any options +required by Sail itself. As an example, the file for v8.5 is +```json +{ + "options" : "-non_lexical_flow -no_lexp_bounds_check", + "files" : [ + "prelude.sail", + "no_devices.sail", + "aarch_types.sail", + "aarch_mem.sail", + "aarch64.sail", + "aarch64_float.sail", + "aarch64_vector.sail", + "aarch32.sail", + "aarch_decode.sail" + ] +} +``` + +For this to work Sail must be build with interactive support as `make +isail`. This requires the yojson library as a new dependency (`opam +install yojson`). + +###### Boolean constraints and type-variables + +We now support Boolean type arguments in much the same way as numeric +type arguments. Much like the type int('n), which means an integer +equal to the type variable 'n, bool('p) now means a Boolean that is +true provided the constraint 'p holds. This enables us to do flow +typing in a less ad-hoc way, as we can now have types like +``` +val operator <= : forall 'n 'm. (int('n), int('n)) -> bool('n <= 'm) +``` +The main use case for this feature in specifications is to support +flags that change the range of type variables, e.g: +``` +val my_op : forall 'n ('f : Bool), 0 <= 'n < 15 & ('f | 'n < 4). + (bool('f), int('n)) -> unit + +function my_op(flag, index) = { + if flag then { + // 0 <= 'n < 15 holds + let x = 0xF[index]; // will fail to typecheck here + ... + } else { + // 0 <= 'n < 4 holds + let x = 0xF[index]; // will typecheck here + ... + } +} +``` + +This change is mostly backwards compatible, except in some cases extra +type annotations may be required when declaring mutable Boolean +variables, so +``` +x = true // declaration of x +x = false // type error because x inferred to have type bool(true) +``` +should become +``` +x : bool = true // declaration of x +x = false // fine because x can have any Boolean value +``` + +###### Simpler implicit arguments + +Function implicit arguments are now given explicitly in their type signatures so +``` +val zero_extend : forall 'n 'm, 'm >= 'n. bits('n) -> bits('m) + +function zero_extend(v) = zeros('m - length(v)) @ v +``` +would now become +``` +val zero_extend : forall 'n 'm, 'm >= 'n. (implicit('m), bits('n)) -> bits('m) + +function zero_extend(m, v) = zeros(m - length(v)) @ v +``` + +This radically simplifies how we resolve such implicit arguments +during type-checking, and speeds up processing large specifications +like ARM v8.5 significantly. + +There is a symbol `FEATURE_IMPLICITS` which can be used with `$ifdef` +to write both new and old-versions if desired for backwards +compatibility, as the new version is syntactically valid in older Sails, +but just doesn't typecheck. + +###### Lem monad embedding changes + +The monad embedding for Lem has been changed to make it more friendly +for theorem proving. This can break model-specific Lem that depends on +the definitions in [src/gen_lib](src/gen_lib). |