5. Changelog for the Clash project

5.1. 1.6.5 Jun 27th 2023


  • Support building with all combinations of specific versions of our dependencies hashable and primitive. #2485

  • The Haskell simulation of the PLL lock signal in Clash.Clocks (used by Clash.Intel.ClockGen) is fixed: the signal is now unasserted for the time the reset input is asserted and vice versa, and no longer crashes the simulation. HDL generation is unchanged. The PLL functions now have an additional constraint: KnownDomain pllLock. #2420


  • Export the constructor for the Wrapping type in the Clash.Num.Wrapping module. See #2292

5.2. 1.6.4 Aug 30th 2022


  • Input validation of the used arguments in blackboxes is now complete. #2184

  • Clash.Annotations.BitRepresentation.Deriving.deriveAnnotation no longer has quadratic complexity in the size of the constructors and fields. #2209

  • Fully resolve type synonyms when deriving bit representations. #2209

  • Disregard ticks when determining whether terms are shared. Fixes #2233.

  • The blackbox parser will make sure it fully parses its input, and report an error when it can’t. #2237

  • Wrap ~ARG[n] in parentheses. Fixes #2213

  • The VHDL shift primitives no longer generate bound check failures. Fixes #2215

  • Evaluator fails impredicative type instantiation of error values #2272

  • Fix out of bound errors in toEnum/fromSLV for sum types #2220

  • Netlist generation fails for certain uses of GADTs #2289

  • The documentation for ANN TestBench had it backwards; it now correctly indicates the annotation is on the test bench, not the device under test. #1750

Fixes with minor changes:

  • reduceXor now produces a result if the argument has undefined bits instead of throwing an XException (the result is an undefined bit). reduceAnd and reduceOr already always produced a result. #2244


  • Support for symbols in types while deriving bit representations. #2209

  • Support for promoted data types while deriving bit representations. #2209

  • scanlPar and scanrPar in Clash’s Prelude, as well as the RTree versions tscanl and tscanr. These variants of scanl1 and scanr1 compile to a binary tree of operations, with a depth of O(log(n)) (n being the length of the vector) rather than a depth of n for scanl1 and scanr1. #2177

  • The GADT constructors for RTree (RLeaf and RBranch) are now exported directly in addition to the patterns LR and BR. #2177

  • Added the ~ISSCALAR template which can be used to check if an argument is rendered to a scalar in HDL. #2184

  • Added support for records and infix constructors when using Clash.Annotations.BitRepresentation.Deriving.deriveAnnotation. #2191

  • Clash now contains instances for ShowX, NFDataX and BitPack on the newtypes from the Data.Functor modules (Identity, Const, Compose, Product and Sum). #2218

5.3. 1.6.3 Apr 7th 2022


  • Handle ~ISUNDEFINED hole in black boxes for BitVector and for product types. This means that with -fclash-aggressive-x-optimization-blackboxes, resets are now omitted for undefined reset values of such types as well. #2117

  • The alteraPll primitive was unusable since commit d325557750 (release v1.4.0), it now works again. #2136

  • Simulation/Synthesis mismatch for X-exception to undefined bitvector conversion #2154

  • The VHDL blackbox for Signed.fromInteger can now handle any Netlist Expr as input #2149

  • Clash no longer escapes extended identifiers when rendering SDC files. #2142

  • The types defined in clash-prelude-hedgehog now come with Show instances #2133

  • Extreme values are now generated from the input range instead of the type’s bounds #2138

Internal change:

  • Clash now always generates non-extended identifiers for port names, so that generated names play nicer with different vendor tools. #2142

  • Top entity name available in netlist context. Top entity name used in generated name for include files. #2146

5.4. 1.6.2 Feb 25th 2022


  • Clash now compiles for users of Clang - i.e., all macOS users.

  • The trueDualPortBlockRam model did not accurately simulate concurrent active ports, thus causing a Haskell/HDL simulation mismatch for asyncFIFOSynchronizer.

  • trueDualPortBlockRam Haskell/HDL simulation mismatch for port enable.

  • Sometimes trueDualPortBlockRam swapped the names of the ports in exception messages. #2102

  • The evaluator rule for unpack{Float,Double}# are now corrected to return boxed float and double instead of unboxed literals. #2097


  • The trueDualPortBlockRam model now only models read/write conflicts for concurrent active ports

  • The trueDualPortBlockRam model now models write/write conflicts for concurrent active ports

5.5. 1.6.1 Feb 11th 2022


  • We accidentally released v1.6.0 with the Cabal flag multiple-hidden enabled. This is an experimental feature, supposed to be disabled by default for releases. v1.6.1 disables it again.


  • Clash.Class.HasDomain.TryDomain instances for Clash sized types

5.6. 1.6.0 Feb 10th 2022


  • Clash.Class.Counter: a class that defines a odometer-style supercounter. #1763

  • isLike function for BitPack types. #1774

  • ‘seqErrorX’ for catching both XException and ErrorCall. #1774

  • Clash.Explicit.BlockRam.File.memFile, a function for creating the contents of the data files this blockRAM uses. Can also be imported from Clash.Prelude.BlockRam.File, Clash.Prelude.ROM.File and Clash.Explicit.ROM.File. #1840

  • Support for Yosys compatible SVA to Clash.Verification. This enables formal verification using SymbiYosis for Verilog and SystemVerilog. #1798

  • Clash.Explicit.Signal.Delayed.forward, a function that can be used to retime a DSignal into the future without applying any logic. #1882

  • Clash.Signal.andEnable is the HiddenEnable version of Clash.Explicit.Signal.andEnable (formerly known as enable) #1849

  • runUntil, a function to sample a signal until it returns a value that satisfies the user-given test. It is a convenience function that, among others, allow easy running of a testBench style function in Haskell simulation, logging assertion failures to stderr. #1940

  • Support for true dual ported block ram through Clash.Prelude.BlockRam.trueDualPortBlockRam and Clash.Explicit.BlockRam.trueDualPortBlockRam. #1726 #1975

  • clash-{prelude,lib}-hedgehog packages which provide generators for types in clash-prelude and clash-lib. The former is published on Hackage. #1976

  • Clash now contains black boxes which are verilator compatible. When running with --verilog or --systemverilog a C++ shim is automatically produced which can be used to quickly generate a verilated executable. Users who wish to interact with verilator simulations are recommended to use clashilator. #2019

  • Support for YAML blackboxes. Clash will now pickup on files with a .primitives.yaml extension. While we recommend upgrading your primitive files to the new format, old style primitives are still supported. We’ve included a tool to automatically upgrade your JSON files, see #2037

  • MemBlob: a datastructure for efficient constants, typically used for initializing memories. #2041


  • BlockRam simulation is now less strict. #1458

  • Don’t overflow VHDL’s integer type when addressing RAM/ROM in simulation.Addresses are masked to 32 bits to be sure to keep it within the simulator’s range. #1875

  • show on BitVector 0 no longer results in an empty string. #1785

  • Clash now preserves transfinite floating numbers (NaN, Infinity) when packing/unpacking #1803

  • SynthesisAnnotations can now be defined in type synoynms without being excluded from the generated HDL #1771

  • Manifest files now correctly list bidirectional ports as “inout” rather than “in” #1843

  • div/rem/mod now avoid division by zero during VHDL simulation. Due to the use of concurrent statements, even unreachable code would previously result in simulation error #1873

  • Don’t overflow the range of VHDL’s natural type in shift/rotate, leading to simulation issues. Shift now saturates to a 31-bit shift amount. For rotate, in simulation only, the rotate amount is modulo the word width of the rotated value #1874

  • shiftL for Clash datatypes does not cause a crash anymore when running Clash code with a really large shift amount #1874

  • VHDL generated for Signed.fromInteger now truncates, like the Clash simulation, when the result is smaller than the argument #1874

  • Clash now preserves boolean combinatorial logic better when generating HDL #1881

  • valid field of TemplateFunction is now checked for includes #1945

  • Clash now generates clock generators that ensure that the amount of time between simulation start and the first active edge of the clock is equal to (/or longer than/) the period of the clock. The first active edges of the clocks do still occur simultaneously. #2001

  • Expected values in assert become undefined when using -fclash-compile-ultra #2040

  • toEnum/fromEnum on sized types is now less eager to report warnings about integer functions being used #2046


  • Clash.Verification.PrettyPrinters has been moved from clash-prelude to to Clash.Verification.Pretty in clash-lib. #1798

  • RAM/ROM functions: They now throw XExeception for out-of-bounds address inputs, so this condition no longer aborts simulation. #1875

  • Vec’s show instance now generates valid Haskell. #1776

  • ShowX and its functions now produce valid Haskell #1782

  • bLit now infers the size of the generated BitVector from the string given to it. This means you don’t have to give it an explicit type signature anymore. This does slightly modify the syntax needed to invoke bLit. E.g., $$(bLit "00..1") :: BitVector 5 should be rewritten as $(bLit "00..1"). If you relied on the size inference, wrap the new invocation in resize. For example: resize $(bLit "00..1"). #1784

  • NumericUnderscores is now enabled by default in clash, clashi, and starter projects using Clash >=1.6. #1785

  • Show instance of BitVector now includes a 0b prefix, making it a copyable expression for fully defined vectors. #1785

  • blockRam uses STArray as the underlying representation to improve simulation performance #1878

  • asyncRom now throws XException for out-of-bounds addressing, no longer aborting simulation #1878

  • Clash now renders ADTs with all zero-width fields as enumerations in VHDL #1879

  • A warning about possible hard-to-debug issues has been added to the Clash.Signal documentation on hidden clocks, resets, and enables, in the form of the section named “Monomorphism restriction leads to surprising behavior” #1960

  • Clash.Explicit.Testbench.outputVerifier and outputVerifierBitVector now emit a warning if they are used improperly. This situation only arises when they are used in synthesized code rather than a test bench context. When the clock domains circuitDom and testDom are two different domains, the clock crossing inside outputVerifier is only suitable inside a test bench, not inside a synthesized circuit. Clash now emits a warning for this case. #1931

  • resetSynchronizer now no longer takes an Enable argument. The argument was already marked for removal and was ignored. #1964

  • Clash can now compile multiple entities concurrently, providing speedups to designs with multiple entities to build #2034

  • All asyncRam variants and asyncFIFOSynchronizer now require that the data has an NFDataX instance. #2055

  • Clash now respects the -Werror option from GHC #2066

  • asyncFIFOSynchronizer now uses the synchronous dual-ported RAM trueDualPortBlockRam, where it previously used a dual-ported RAM with an asynchronous read port asyncRam. With this change it’s nearly guaranteed that asyncFIFOSynchronizer actually synthesizes to a circuit that uses the dual-ported RAMs found on most FPGAs. #2083


  • The function Clash.Explicit.Signal.enable is renamed to andEnable and the existing name deprecated #1849

  • ‘-fclash-float-support’: it is now on by default and can’t be turned off. #2048


  • GHC 8.4 is no longer supported. Users should upgrade to at least GHC 8.6. #1762

Internal changes:

  • clash-lib now uses Data.Monoid.Ap instead of Data.Semigroup.Monad.Mon. This means users defining primitives with TemplateFunction will need to replace Mon/getMon with Ap/getAp. #1835

  • Clash now supports more expressive debug options at the command line #1800.

  • Added zeroWidthSpec transformation #1891

  • Added collapseRHSNoops inlining stage and WorkIdentity constructor #1896

  • Added HasType and InferType classes for getting / inferring core types from data representing some typed “thing” #1915

  • Added HasFreeVars class for getting free variables from data “containing” variables #1917

  • Added the primitive equality type (~#) to Clash.Core.TysPrim. In order to make this change, undefinedTy and unsafeCoerceTy were moved from Clash.Core.Type to Clash.Core.Util. #1955

  • Clash now keeps information about which let bindings are recursive from GHC core. This can be used to avoid performing free variable calculations, or sorting bindings in normalization. #1980 #2000

  • Manifest files now use SHA256 for a cache invalidation digest #1985

5.7. 1.4.7 Jan 30th 2022


  • Clash now shows days in time strings for compile runs which take longer than a day #1989.

  • Types defined in the package head are no longer qualified in the package body when rendering VHDL #1996.

  • asyncRam with different read and write clocks no longer produce the wrong results in Haskell simulation. #2031

  • Clash.Explicit.RAM.asyncRam# Haskell simulation incorrectly treated an undefined write enable as asserted. It now causes an undefined value to be written instead. This problem did not propagate to the other asyncRam functions, where the same condition would simultaneously lead to an undefined write address, which would be handled correctly. This problem also only affects Haskell simulation, not the generated HDL. #2031

  • Clash.Explicit.BlockRam.blockRam# and Clash.Explicit.BlockRam.File.blockRamFile# Haskell simulation incorrectly treated an undefined write enable as asserted. It now causes an undefined value to be written instead. This problem did not propagate to the other blockRam functions, where the same condition would simultaneously lead to an undefined write address, which would be handled correctly. This problem also only affects Haskell simulation, not the generated HDL.(#2054)

Internal changes:

  • Removed instances of Hashable Term and Hashable Type #1986

  • Added structural equality on Term (Clash.Core.Subst.eqTerm) and Type (Clash.Core.Subst.eqType)

Internal fixes:

  • Enable used to be a Bool in the Blackbox DSL, so we could use boolToBit. However it now has its own type in the DSL (Enable domainName), so we’ve added a new conversion function in order to convert it to a Bool.

5.8. 1.4.6 Oct 26th 2021


  • Clash tries to cast-specialize non-“global binders” resulting in “specialisation of non-work-free cast” warning #1933

  • More consistently render bare untyped and unsized literals for ~LIT tags. This fixes #1934

5.9. 1.4.5 Oct 13th 2021


  • clash-lib now supports prettyprinter 1.7


  • The documentation on hidden clocks, resets, and enables has been corrected and extended in Clash.Signal.

5.10. 1.4.4 Oct 11th 2021


  • clash-lib now supports aeson >= 2.0


  • Dont’ loop on recursive data types hiding behind type families #1921

  • Recognize enableGen as workfree and don’t duplicate registers #1935

5.11. 1.4.3 Aug 8th 2021


  • Clash no longer generates calls to {shift,rotate}_{left,right} in VHDL where the count is a negative number #1810.

  • Clash no longer incurs unnecessary compile-time complexity while compiling Vector indexing operator #1557

5.12. 1.4.2 May 18th 2021


  • Erroneous examples in Clash.Annotation.TopEntity documentation #646 and #654

  • unconcat cannot be used as initial/reset value for a register #1756

  • showX now doesn’t crash if a spine of a Vec is undefined

  • ~ISACTIVEENABLE in blackboxes works again, and now acts on Signal dom Bool in addition to Enable dom. Since #1368, enable lines were always generated even if they were known to be always enabled. Fixes #1786.

  • clash –show-options now shows -fclash-* options in GHC 9.0 #1787

  • makeRecursiveGroups now correctly identifies mutual recursion between global binders (#1796).

5.13. 1.4.1 April 6th 2021


  • Broken VHDL primitive template for setSlice# #1715

  • Unable to reduce nested type families #1721

  • DEC transformation fails for functions applied to more than 62 arguments #1669

  • Erroneous examples in BlockRam.File and ROM.File documentation #1608

  • Blackboxes of Clash.Sized.Vector functions error on vectors containing Clocks, Reset, or Enable #1606

  • Clash.Signal.Delayed.delayI cannot be reset, the HiddenReset constraint was unintentional. Asserting its reset has never worked. Removed the constraint #1739.

  • Annotate attributes cannot use type families #1742


  • Clash.Prelude.ROM.File.romFile now takes an Enum addr => addr as address argument, making it actually useful. #407

5.14. 1.4.0 March 12th 2021

Highlighted changes (repeated in other categories):

  • Clash no longer disables the monomorphism restriction. See #1270, and mentioned issues, as to why. This can cause, among other things, certain eta-reduced descriptions of sequential circuits to no longer type-check. See #1349 for code hints on what kind of changes to make to your own code in case it no longer type-checks due to this change.

  • Type arguments of Clash.Sized.Vector.fold swapped: before forall a n . (a -> a -> a) -> Vec (n+1) a -> a, after forall n a . (a -> a -> a) -> Vec (n+1) a. This makes it easier to use fold in a 1 <= n context so you can “simply” do fold @(n-1)

  • Fixed now obeys the laws for Enum as set out in the Haskell Report, and it is now consistent with the documentation for the Enum class on Hackage. As Fixed is also Bounded, the rule in the Report that succ maxBound and pred minBound should result in a runtime error is interpreted as meaning that succ and pred result in a runtime error whenever the result cannot be represented, not merely for minBound and maxBound alone.

  • Primitives should now be stored in *.primitives files instead of *.json. While primitive files very much look like JSON files, they’re not actually spec complaint as they use newlines in strings. This has recently been brought to our attention by Aeson fixing an oversight in their parser implementation. We’ve therefore decided to rename the extension to prevent confusion.


  • Result of Clash.Class.Exp.(^) has enough bits in order to deal with x^0.

  • Resizes to Signed 0 (e.g., resize @(Signed n) @(Signed 0)) don’t throw an error anymore

  • satMul now correctly handles arguments of type Index 2

  • Clash.Explicit.Reset.resetSynchronizer now synchronizes on synchronous domains too #1567.

  • Clash.Explicit.Reset.convertReset: now converts synchronous domains too, if necessary #1567.

  • inlineWorkFree now never inlines a topentity. It previously only respected this invariant in one of the two cases #1587.

  • Clash now reduces recursive type families #1591

  • Primitive template warning is now retained when a PrimitiveGuard annotation is present #1625

  • signum and RealFrac for Fixed now give the correct results.

  • Fixed a memory leak in register when used on asynchronous domains. Although the memory leak has always been there, it was only triggered on asserted resets. These periods are typically short, hence typically unnoticable.

  • createDomain will not override user definitions of types, helping users who strive for complete documentation coverage [#1674] https://github.com/clash-lang/clash-compiler/issues/1674

  • fromSNat is now properly constrained #1692

  • As part of an internal overhaul on netlist identifier generation #1265:

    • Clash no longer produces “name conflicts” between basic and extended identifiers. I.e., \x\ and x are now considered the same variable in VHDL (likewise for other HDLs). Although the VHDL spec considers them distinct variables, some HDL tools - like Quartus - don’t.

    • Capitalization of Haskell names are now preserved in VHDL. Note that VHDL is a case insensitive languages, so there are measures in place to prevent Clash from generating both Foo and fOO. This used to be handled by promoting every capitalized identifier to an extended one and wasn’t handled for basic ones.

    • Names generated for testbenches can no longer cause collisions with previously generated entities.

    • Names generated for components can no longer cause collisions with user specified top entity names.

    • For (System)Verilog, variables can no longer cause collisions with (to be) generated entity names.

    • HO blackboxes can no longer cause collisions with identifiers declared in their surrounding architecture block.


  • Treat enable lines specially in generated HDL #1171

  • Signed, Unsigned, SFixed, and UFixed now correctly implement the Enum law specifying that the predecessor of minBound and the successor of maxBound should result in an error #1495.

  • Fixed now obeys the laws for Enum as set out in the Haskell Report, and it is now consistent with the documentation for the Enum class on Hackage. As Fixed is also Bounded, the rule in the Report that succ maxBound and pred minBound should result in a runtime error is interpreted as meaning that succ and pred result in a runtime error whenever the result cannot be represented, not merely for minBound and maxBound alone.

  • Type arguments of Clash.Sized.Vector.fold swapped: before forall a n . (a -> a -> a) -> Vec (n+1) a -> a, after forall n a . (a -> a -> a) -> Vec (n+1) a. This makes it easier to use fold in a 1 <= n context so you can “simply” do fold @(n-1)

  • Moved Clash.Core.Evaluator into Clash.GHC and provided generic interface in Clash.Core.Evalautor.Types. This removes all GHC specific code from the evaluator in clash-lib.

  • Clash no longer disables the monomorphism restriction. See #1270, and mentioned issues, as to why. This can cause, among other things, certain eta-reduced descriptions of sequential circuits to no longer type-check. See #1349 for code hints on what kind of changes to make to your own code in case it no longer type-checks due to this change.

  • Clash now generates SDC files for each topentity with clock inputs

  • deepErrorX is now equal to undefined#, which means that instead of the whole BitVector being undefined, its individual bits are. This makes sure bit operations are possible on it. #1532

  • From GHC 9.0.1 onwards the following types: BiSignalOut, Index, Signed, Unsigned, File, Ref, and SimIO are all encoded as data instead of newtype to work around an issue where the Clash compiler can no longer recognize primitives over these types. This means you can no longer use Data.Coerce.coerce to coerce between these types and their underlying representation.

  • Signals on different domains used to be coercable because the domain had a type role “phantom”. This has been changed to “nominal” to prevent accidental, unsafe coercions. #1640

  • Size parameters on types in Clash.Sized.Internal.* are now nominal to prevent unsafe coercions. #1640

  • hzToPeriod now takes a Ratio Natural rather than a Double. It rounds slightly differently, leading to more intuitive results and satisfying the requested change in #1253. Clash expresses clock rate as the clock period in picoseconds. If picosecond precision is required for your design, please use the exact method of specifying a clock period rather than a clock frequency.

  • periodToHz now results in a Ratio Natural

  • createDomain doesn’t override existing definitions anymore, fixing #1674

  • Manifest files are now stored as clash-manifest.json

  • Manifest files now store hashes of the files Clash generated. This allows Clash to detect user changes on a next run, preventing accidental data loss.

  • Primitives should now be stored in *.primitives files. While primitive files very much look like JSON files, they’re not actually spec complaint as they use newlines in strings. This has recently been brought to our attention by Aeson fixing an oversight in their parser implementation. We’ve therefore decided to rename the extension to prevent confusion.

  • Each binder marked with a Synthesize or TestBench pragma will be put in its own directory under their fully qualified Haskell name. For example, two binders foo and bar in module A will be synthesized in A.foo and A.bar.

  • Clash will no longer generate vhdl, verilog, or systemverilog subdirectories when using -fclash-hdldir.

  • Data.Kind.Type is now exported from Clash.Prelude #1700


  • Support for GHC 9.0.1

  • Clash.Signal.sameDomain: Allows user obtain evidence whether two domains are equal.

  • xToErrorCtx: makes it easier to track the origin of XException where pack would hide them #1461

  • Additional field with synthesis attributes added to InstDecl in Clash.Netlist.Types #1482

  • Data.Ix.Ix instances for Signed, Unsigned, and Index #1481 #1631

  • Added nameHint to allow explicitly naming terms, e.g. Signals.

  • Checked versions of resize, truncateB, and fromIntegral. Depending on the type resize, truncateB, and fromIntegral either yield an XException or silently perform wrap-around if its argument does not fit in the resulting type’s bounds. The added functions check the bound condition and fail with an error call if the condition is violated. They do not affect HDL generation. #1491

  • HasBiSignalDefault: constraint to Clash.Signal.BiSignal, pullUpMode gives access to the pull-up mode. #1498

  • Match patterns to bitPattern #1545

  • Non TH fromList and unsafeFromList for Vec. These functions allow Vectors to be created from a list without needing to use template haskell, which is not always desirable. The unsafe version of the function does not compare the length of the list to the desired length of the vector, either truncating or padding with undefined if the lengths differ.

  • Clash.Explicit.Reset.resetGlitchFilter: filters glitchy reset signals. Useful when your reset signal is connected to sensitive actuators.

  • Clash can now generate EDAM for using Edalize. This generates edam.py files in all top entities with the configuration for building that entity. Users still need to edit this file to specify the EDA tool to use, and if necessary the device to target (for Quartus, Vivado etc.). #1386

  • -fclash-aggressive-x-optimization-blackboxes: when enabled primitives can detect undefined values and change their behavior accordingly. For example, if register is used in combination with an undefined reset value, it will leave out the reset logic entirely. Related issue: #1506.

  • Automaton-based interface to simulation, to allow interleaving of cyle-by-cycle simulation and external effects #1261

New internal features:

  • constructProduct and deconstructProduct in Clash.Primitives.DSL. Like tuple and untuple, but on arbitrary product types.

  • Support for multi result primitives. Primitives can now assign their results to multiple variables. This can help to work around synthesis tools limits in some cases. See #1560.

  • Added a rule for missing Int comparisons in GHC.Classes in the compile time evaluator. #1648

  • Clash now creates a mapping from domain names to configurations in LoadModules. #1405

  • The convenience functions in Clash.Primitives.DSL now take a list of HDLs, instead of just one.

  • Clash.Netlist.Id overhauls the way identifiers are generated in the Netlist part of Clash.

  • Added defaultWithAction to Clash-as-a-library API to work around/fix issues such as #1686

  • Manifest files now list files and components in an reverse topological order. This means it can be used when calling EDA tooling without causing compilation issues.


  • Clash.Prelude.DataFlow: see #1490. In time, its functionality will be replaced by clash-protocols.


  • The deprecated function freqCalc has been removed.

5.15. 1.2.5 November 9th 2020


  • The normalizeType function now fully normalizes types which require calls to reduceTypeFamily #1469

  • flogBaseSNat, clogBaseSNat and logBaseSNat primitives are now implemented correctly.Previously these primitives would be left unevaluated causing issues as demonstrated in #1479

  • Specializing on functions with type family arguments no longer fails #1477

  • satSucc, satPred correctly handle “small types” such as Index 1.

  • msb no longer fails on values larger than 64 bits

  • undefined can now be used as a reset value of autoReg@Maybe #1507

  • Signal’s fmap is now less strict, preventing infinite loops in very specific situations. See #1521

  • Clash now uses correct function names in manifest and sdc files #1533

  • Clash no longer produces erroneous HDL in very specific cases #1536

  • Usage of fold inside other HO primitives (e.g., map) no longer fails #1524


  • Due to difficulties using resetSynchronizer we’ve decided to make this function always insert a synchronizer. See: #1528.

5.16. 1.2.4 July 28th 2020

  • Changed:

    • Relaxed upper bound versions of aeson and dlist, in preparation for the new Stack LTS.

    • Reverted changes to primitive definitions for ‘zipWith’, ‘map’, ‘foldr’, and ‘init’ introduced in 1.2.2. They have shown to cause problems in very specific circumstances.

5.17. 1.2.3 July 11th 2020

  • Changed:

    • Upgrade to nixos 20.03. Nix and snap users will now use packages present in 20.03.

  • Added:

    • instance Monoid a => Monoid (Vec n a)

    • instance Text.Printf(Index)

    • instance Text.Printf(Signed)

    • instance Text.Printf(Unsigned)

  • Fixed:

    • Clash renders incorrect VHDL when GHCs Worker/Wrapper transformation is enabled #1402

    • Minor faults in generated HDL when using annotations from Clash.Annotations.SynthesisAttributes

    • Cabal installed through Snap (clash.cabal) can now access the internet to fetch pacakges. [#1411]https://github.com/clash-lang/clash-compiler/issues/1411

    • Generated QSys file for altpll incompatible with Quartus CLI (did work in Quartus GUI)

    • Clash no longer uses component names that clash with identifiers imported from:

      • IEEE.STD_LOGIC_1164.all

      • IEEE.NUMERIC_STD.all

      • IEEE.MATH_REAL.all

      • std.textio.all when generating VHDL. See https://github.com/clash-lang/clash-compiler/issues/1439.

5.18. 1.2.2 June 12th 2020

  • Changed:

    • The hardwired functions to unroll primitive definitions for ‘zipWith’, ‘map’, ‘foldr’, and ‘init’ have been changed to only unroll a single step, whereas they would previously unroll the whole definition in one step. This allows Clash to take advantage of the lazy nature of these functions, in turn speeding up compilation speeds significantly in some cases. Part of PR 1354.

  • Added:

    • Support for GHC 8.10

    • Ability to load designs from precompiled modules (i.e., stored in a package database). See #1172

    • Support for ‘-main-is’ when used with --vhdl, --verilog, or --systemverilog

    • A partial instance for NFDataX (Signal domain a)

  • Fixed:

    • Clash’s evaluator now inlines work free definitions, preventing situations where it would otherwise get stuck in an infinite loop

    • caseCon doesn’t apply type-substitution correctly #1340

    • Clash generates illegal SystemVerilog slice #1313

    • Fix result type of head and tail Verilog blackboxes #1351

    • Certain recursive let-expressions in side a alternatives of a case-expression throw the Clash compiler into an infinite loop #1316

    • Fixes issue with one of Clash’s transformations, inlineCleanup, introducing free variables #1337

    • Fails to propagate type information of existential type #1310

    • Certain case-expressions throw the Clash compiler into an infinite loop #1320

    • Added blackbox implementation for ‘Clash.Sized.Vector.iterateI’, hence making it usable as a register reset value #1240

    • iterate and iterateI can now be used in reset values #1240

    • Prim evaluation fails on undefined arguments #1297

    • Missing re-indexing in (Un)Signed fromSLV conversion #1292

    • VHDL: generate a type qualification inside ~TOBV, fixes #1360

5.19. 1.2.1 April 23rd 2020

  • Changed:

    • Treat Signed 0, Unsigned 0, Index 1, BitVector 0 as unit. In effect this means that ‘minBound’ and ‘maxBound’ return 0, whereas previously they might crash #1183

    • Infix use of deepseqX is now right-associative

  • Added:

    • Add ‘natToInteger’, ‘natToNatural’, and ‘natToNum’. Similar to ‘snatTo*’, but works solely on a type argument instead of an SNat.

    • Clash.Sized.Vector.unfoldr and Clash.Sized.Vector.unfoldrI to construct vectors from a seed value

    • Added NFDataX instances for Data.Monoid.{First,Last}

  • Fixed:

    • The Verilog backend can now deal with non-contiguous ranges in custom bit-representations.

    • Synthesizing BitPack instances for type with phantom parameter fails #1242

    • Synthesis of fromBNat (toBNat d5) failed due to unsafeCoerce coercing from Any

    • Memory leak in register primitives #1256

    • Illegal VHDL slice when projecting nested SOP type #1254

    • Vivado VHDL code path (-fclash-hdlsyn Vivado) generates illegal VHDL #1264

5.20. 1.2.0 March 5th 2020

As promised when releasing 1.0, we’ve tried our best to keep the API stable. We think most designs will continue to compile with this new version, although special care needs to be taken when using:

  • Use inline blackboxes. Instead of taking a single HDL, inline primitives now take multiple. For example, InlinePrimitive VHDL ".." must now be written as InlinePrimitive [VHDL] "..".

  • Use the Enum instance for BitVector, Index, Signed, or Unsigned, as they now respect their maxBound. See #1089.

On top of that, we’ve added a number of new features:

  • makeTopEntity: Template Haskell function for generating TopEntity annotations. See the documentation on Haddock for more information.

  • Clash.Explicit.SimIO: ((System)Verilog only) I/O actions that can be translated to HDL I/O. See the documentation on Haddock for more information.

  • Clash.Class.AutoReg: A smart register that improves the chances of synthesis tools inferring clock-gated registers, when used. See the documentation on Haddock for more information.

The full list of changes follows. Happy hacking!

  • New features (API):

    • Clash.Class.Parity type class replaces Prelude odd and even functions due to assumptions that don’t hold for Clash specific numerical types, see #970.

    • NFDataX.ensureSpine, see #748

    • makeTopEntity Template Haskell function for generating TopEntity annotations intended to cover the majority of use cases. Generation failures should either result in an explicit error, or a valid annotation of an empty PortProduct. Any discrepancy between the shape of generated annotations and the shape of the Clash compiler is a bug. See #795. Known limitations:

      • Type application (excluding Signals and :::) is best effort:

      • Data types with type parameters will work if the generator can discover a single relevant constructor after attempting type application.

      • Arbitrary explicit clock/reset/enables are supported, but only a single HiddenClockResetEnable constraint is supported.

      • Data/type family support is best effort.

    • Added Bundle ((f :*: g) a) instance

    • Added NFDataX CUShort instance

    • Clash’s internal type family solver now recognizes AppendSymbol and CmpSymbol

    • Added Clash.Magic.suffixNameFromNat: can be used in cases where suffixName is too slow

    • Added Clash.Class.AutoReg. Improves the chances of synthesis tools inferring clock-gated registers, when used. See #873.

    • Clash.Magic.suffixNameP, Clash.Magic.suffixNameFromNatP: enable prefixing of name suffixes

    • Added Clash.Magic.noDeDup: can be used to instruct Clash to /not/ share a function between multiple branches

    • A BitPack a constraint now implies a KnownNat (BitSize a) constraint, so you won’t have to add it manually anymore. See #942.

    • Clash.Explicit.SimIO: ((System)Verilog only) I/O actions that can be translated to HDL I/O; useful for generated test benches.

    • Export Clash.Explicit.Testbench.assertBitVector #888

    • Add Clash.Prelude.Testbench.assertBitVector to achieve feature parity with Clash.Explicit.Testbench. #891

    • Add Clash.XException.NFDataX.ensureSpine #803

    • Add Clash.Class.BitPack.bitCoerceMap #798

    • Add Clash.Magic.deDup: instruct Clash to force sharing an operator between multiple branches of a case-expression

    • InlinePrimitive can now support multiple backends simultaneously #425

    • Add Clash.XException.hwSeqX: render declarations of an argument, but don’t assign it to a result signal

    • Add Clash.Signal.Bundle.TaggedEmptyTuple: allows users to emulate the pre-1.0 behavior of “Bundle ()”. See #1100

  • New features (Compiler):

    • #961: Show -fclash-* Options in clash --show-options

  • New internal features:

    • #918: Add X-Optimization to normalization passes (-fclash-aggressive-x-optimization)

    • #821: Add DebugTry: print name of all tried transformations, even if they didn’t succeed

    • #856: Add -fclash-debug-transformations: only print debug info for specific transformations

    • #911: Add ‘RenderVoid’ option to blackboxes

    • #958: Prefix names of inlined functions

    • #947: Add “Clash.Core.TermLiteral”

    • #887: Show nicer error messages when failing in TH code

    • #884: Teach reduceTypeFamily about AppendSymbol and CmpSymbol

    • #784: Print whether Id is global or local in ppr output

    • #781: Use naming contexts in register names

    • #1061: Add ‘usedArguments’ to BlackBoxHaskell blackboxes

  • Fixes issues:

    • #974: Fix indirect shadowing in reduceNonRepPrim

    • #964: SaturatingNum instance of Index now behaves correctly when the size of the index overflows an Int.

    • #810: Verilog backend now correctly specifies type of BitVector 1

    • #811: Improve module load behavior in clashi

    • #439: Template Haskell splices and TopEntity annotations can now be used in clashi

    • #662: Clash will now constant specialize partially constant constructs

    • #700: Check work content of expression in cast before warning users. Should eliminate a lot of (superfluous) warnings about “specializing on non work-free cast”s.

    • #837: Blackboxes will now report clearer error messages if they’re given unexpected arguments.

    • #869: PLL is no longer duplicated in Blinker.hs example

    • #749: Clash’s dependencies now all work with GHC 8.8, allowing clash-{prelude,lib,ghc} to be compiled from Hackage soon.

    • #871: RTree Bundle instance is now properly lazy

    • #895: VHDL type error when generating Maybe (Vec 2 (Signed 8), Index 1)

    • #880: Custom bit representations can now be used on product types too

    • #976: Prevent shadowing in Clash’s core evaluator

    • #1007: Can’t translate domain tagType.Errors.IfStuck…

    • #967: Naming registers disconnects their output

    • #990: Internal shadowing bug results in incorrect HDL

    • #945: Rewrite rules for Vec Applicative Functor

    • #919: Clash generating invalid Verilog after Vec operations #919

    • #996: Ambiguous clock when using ClearOnReset and resetGen together

    • #701: Unexpected behaviour with the Synthesize annotation

    • #694: Custom bit representation error only with VHDL

    • #347: topEntity synthesis fails due to insufficient type-level normalisation

    • #626: Missing Clash.Explicit.Prelude definitions

    • #960: Blackbox Error Caused by Simple map

    • #1012: Case-let doesn’t look through ticks

    • #430: Issue warning when not compiled with executable-dynamic: True

    • #374: Clash.Sized.Fixed: fromInteger and fromRational don’t saturate correctly

    • #836: Generate warning when toInteger blackbox drops MSBs

    • #1019: Clash breaks on constants defined in terms of GHC.Natural.gcdNatural

    • #1025: inlineCleanupwill not produce empty letrecs anymore

    • #1030: bindConstantVar will bind (workfree) constructs

    • #1034: Error (10137): object “pllLock” on lhs must have a variable data type

    • #1046: Don’t confuse term/type namespaces in ‘lookupIdSubst’

    • #1041: Nested product types incorrectly decomposed into ports

    • #1058: Prevent substitution warning when using type equalities in top entities

    • #1033: Fix issue where Clash breaks when using Clock/Reset/Enable in product types in combination with Synthesize annotations

    • #1075: Removed superfluous constraints on ‘maybeX’ and ‘maybeIsX’

    • #1085: Suggest exporting topentities if they can’t be found in a module

    • #1065: Report polymorphic topEntities as errors

    • #1089: Respect maxBound in Enum instances for BitVector,Index,Signed,Unsigned

  • Fixes without issue reports:

    • Fix bug in rnfX defined for Down (baef30e)

    • Render numbers inside gensym (bc76f0f)

    • Report blackbox name when encountering an error in ‘setSym’ (#858)

    • Fix blackbox issues causing Clash to generate invalid HDL (#865)

    • Treat types with a zero-width custom bit representation like other zero-width constructs (#874)

    • TH code for auto deriving bit representations now produces nicer error messages (7190793)

    • Adds ‘–enable-shared-executables’ for nix builds; this should make Clash run much faster (#894)

    • Custom bit representations can now mark fields as zero-width without crashing the compiler (#898)

    • Throw an error if there’s data left to parse after successfully parsing a valid JSON construct (#904)

    • Data.gfoldl is now manually implemented, in turn fixing issues with gshow (#933)

    • Fix a number of issues with blackbox implementations (#934)

    • Don’t inline registers with non-constant clock and reset (#998)

    • Inline let-binders called [dsN | N <- [1..]] (#992)

    • ClockGens use their name at the Haskell level #827

    • Render numbers inside gensym #809

    • Don’t overwrite existing binders when specializing #790

    • Deshadow in ‘caseCase’ #1067

    • Deshadow in ‘caseLet’ and ‘nonRepANF’ #1071

  • Deprecations & removals:

    • Removed support for GHC 8.2 (#842)

    • Removed support for older cabal versions, only Cabal >=2.2 supported (#851)

    • Reset and Enable constructors are now only exported from Clash.Signal.Internal

    • #986 Remove -fclash-allow-zero-width flag

5.21. 1.0.0 September 3rd 2019

  • 10x - 50x faster compile times

  • New features:

    • API changes: check the migration guide at the end of Clash.Tutorial

    • All memory elements now have an (implicit) enable line; “Gated” clocks have been removed as the clock wasn’t actually gated, but implemented as an enable line.

    • Circuit domains are now configurable in:

      • (old) The clock period

      • (new) Clock edge on which memory elements latch their inputs (rising edge or falling edge)

      • (new) Whether the reset port of a memory element is level sensitive asynchronous reset) or edge sensitive (synchronous reset)

      • (new) Whether the reset port of a memory element is active-high or active-low (negated reset)

      • (new) Whether memory element power on in a configurable/defined state (common on FPGAs) or in an undefined state (ASICs)

      • See the blog post on this new feature

    • Data types can now be given custom bit-representations: http://hackage.haskell.org/package/clash-prelude/docs/Clash-Annotations-BitRepresentation.html

    • Annotate expressions with attributes that persist in the generated HDL, e.g. synthesis directives: http://hackage.haskell.org/package/clash-prelude/docs/Clash-Annotations-SynthesisAttributes.html

    • Control (System)Verilog module instance, and VHDL entity instantiation names in generated code: http://hackage.haskell.org/package/clash-prelude/docs/Clash-Magic.html

    • Much improved infrastructure for handling of unknown values: defined spine, but unknown leafs: http://hackage.haskell.org/package/clash-prelude/docs/Clash-XException.html#t:NFDataX

    • Experimental: Multiple hidden clocks. Can be enabled by compiling clash-prelude with -fmultiple-hidden

    • Experimental: Limited GADT support (pattern matching on vectors, or custom GADTs as longs as their usage can be statically removed; no support of recursive GADTs)

    • Experimental: Use regular Haskell functions to generate HDL black boxes for primitives (in an addition to existing string templates for HDL black boxes) See for example: http://hackage.haskell.org/package/clash-lib/docs/Clash-Primitives-Intel-ClockGen.html

  • Fixes issues:

5.22. 0.99.3 July 28th 2018

  • Fixes bugs:

    • Evaluator recognizes Bit literals #329

    • Use existential type-variables in context of GADT pattern match

    • Do not create zero-bit temporary variables in generated HDL

    • Use correct arguments in nested primitives #323

    • Zero-constructor data type needs 0 bits #238

    • Create empty component when result needs 0 bits

    • Evaluator performs BigNat arithmetic

  • Features:

    • Bundle and BitPack instances up to and including 62-tuples

    • Handle undefined writes to RAM properly

    • Handle undefined clock enables properly

5.23. 0.99.1 May 12th 2018

  • Allow ~NAME[N] tag inside ~GENSYM[X]

  • Support HDL record selector generation #313

  • InlinePrimitive support: specify HDL primitives inline with Haskell code

  • Support for ghc-typelits-natnormalise-0.6.1

  • Lift instances for TopEntity and PortName

  • InlinePrimitive support: specify HDL primitives inline with Haskell code

5.24. 0.99 March 31st 2018

  • New features:

    • Major API overhaul: check the migration guide at the end of Clash.Tutorial

    • New features:

      • Explicit clock and reset arguments

      • Rename CLaSH to Clash

      • Implicit/Hidden clock and reset arguments using a combination of reflection and ImplicitParams.

      • Large overhaul of TopEntity annotations

      • PLL and other clock sources can now be instantiated using regular functions: Clash.Intel.ClockGen and Clash.Xilinx.ClockGen.

      • DDR registers:

        • Generic/ASIC: Clash.Explicit.DDR

        • Intel: Clash.Intel.DDR

        • Xilinx: Clash.Intel.Xilinx

    • Bit is now a newtype instead of a type synonym and will be mapped to a HDL scalar instead of an array of one (e.g std_logic instead of std_logic_vector(0 downto 0))

    • Hierarchies with multiple synthesisable boundaries by allowing more than one function in scope to have a Synthesize annotation.

      • Local caching of functions with a Synthesize annotation

    • Bit type is mapped to a HDL scalar type (e.g. std_logic in VHDL)

    • Improved name preservation

    • Zero-bit values are filtered out of the generated HDL

    • Improved compile-time computation

  • Many bug fixes

5.25. Older versions

Check out:

  • https://github.com/clash-lang/clash-compiler/blob/3649a2962415ea8ca2d6f7f5e673b4c14de26b4f/clash-prelude/CHANGELOG.md

  • https://github.com/clash-lang/clash-compiler/blob/3649a2962415ea8ca2d6f7f5e673b4c14de26b4f/clash-lib/CHANGELOG.md

  • https://github.com/clash-lang/clash-compiler/blob/3649a2962415ea8ca2d6f7f5e673b4c14de26b4f/clash-ghc/CHANGELOG.md