The Glorious Glasgow Haskell Compilation System User's Guide, Version 7.6.1.20121125

The GHC Team


Table of Contents

The Glasgow Haskell Compiler License
1. Introduction to GHC
1.1. Obtaining GHC
1.2. Meta-information: Web sites, mailing lists, etc.
1.3. Reporting bugs in GHC
1.4. GHC version numbering policy
1.5. Release notes for version 7.6.1
1.5.1. Highlights
1.5.2. Full details
1.5.2.1. Language
1.5.2.2. Compiler
1.5.2.3. GHCi
1.5.2.4. Template Haskell
1.5.2.5. Runtime system
1.5.2.6. Build system
1.5.3. Libraries
1.5.3.1. array
1.5.3.2. base
1.5.3.3. bin-package-db
1.5.3.4. binary
1.5.3.5. bytestring
1.5.3.6. Cabal
1.5.3.7. containers
1.5.3.8. deepseq
1.5.3.9. directory
1.5.3.10. filepath
1.5.3.11. ghc-prim
1.5.3.12. haskell98
1.5.3.13. haskell2010
1.5.3.14. hoopl
1.5.3.15. hpc
1.5.3.16. integer-gmp
1.5.3.17. old-locale
1.5.3.18. old-time
1.5.3.19. process
1.5.3.20. template-haskell
1.5.3.21. time
1.5.3.22. unix
1.5.3.23. Win32
2. Using GHCi
2.1. Introduction to GHCi
2.2. Loading source files
2.2.1. Modules vs. filenames
2.2.2. Making changes and recompilation
2.3. Loading compiled code
2.4. Interactive evaluation at the prompt
2.4.1. I/O actions at the prompt
2.4.2. Using do-notation at the prompt
2.4.3. Multiline input
2.4.4. Type, class and other declarations
2.4.5. What's really in scope at the prompt?
2.4.5.1. :module and :load
2.4.5.2. Qualified names
2.4.5.3. The :main and :run commands
2.4.6. The it variable
2.4.7. Type defaulting in GHCi
2.4.8. Using a custom interactive printing function
2.5. The GHCi Debugger
2.5.1. Breakpoints and inspecting variables
2.5.1.1. Setting breakpoints
2.5.1.2. Listing and deleting breakpoints
2.5.2. Single-stepping
2.5.3. Nested breakpoints
2.5.4. The _result variable
2.5.5. Tracing and history
2.5.6. Debugging exceptions
2.5.7. Example: inspecting functions
2.5.8. Limitations
2.6. Invoking GHCi
2.6.1. Packages
2.6.2. Extra libraries
2.7. GHCi commands
2.8. The :set and :seti commands
2.8.1. GHCi options
2.8.2. Setting GHC command-line options in GHCi
2.8.3. Setting options for interactive evaluation only
2.9. The .ghci file
2.10. Compiling to object code inside GHCi
2.11. FAQ and Things To Watch Out For
3. Using runghc
3.1. Flags
4. Using GHC
4.1. Getting started: compiling programs
4.2. Options overview
4.2.1. Command-line arguments
4.2.2. Command line options in source files
4.2.3. Setting options in GHCi
4.3. Static, Dynamic, and Mode options
4.4. Meaningful file suffixes
4.5. Modes of operation
4.5.1. Using ghc ––make
4.5.2. Expression evaluation mode
4.5.3. Batch compiler mode
4.5.3.1. Overriding the default behaviour for a file
4.6. Help and verbosity options
4.7. Filenames and separate compilation
4.7.1. Haskell source files
4.7.2. Output files
4.7.3. The search path
4.7.4. Redirecting the compilation output(s)
4.7.5. Keeping Intermediate Files
4.7.6. Redirecting temporary files
4.7.7. Other options related to interface files
4.7.8. The recompilation checker
4.7.9. How to compile mutually recursive modules
4.7.10. Using make
4.7.11. Dependency generation
4.7.12. Orphan modules and instance declarations
4.8. Warnings and sanity-checking
4.9. Packages
4.9.1. Using Packages
4.9.2. The main package
4.9.3. Consequences of packages for the Haskell language
4.9.4. Package Databases
4.9.4.1. The GHC_PACKAGE_PATH environment variable
4.9.5. Package IDs, dependencies, and broken packages
4.9.6. Package management (the ghc-pkg command)
4.9.7. Building a package from Haskell source
4.9.8. InstalledPackageInfo: a package specification
4.10. Optimisation (code improvement)
4.10.1. -O*: convenient “packages” of optimisation flags.
4.10.2. -f*: platform-independent flags
4.11. GHC Backends
4.11.1. Native code Generator (-fasm)
4.11.2. LLVM Code Generator (-fllvm)
4.11.3. C Code Generator (-fvia-C)
4.11.4. Unregisterised compilation
4.12. Options related to a particular phase
4.12.1. Replacing the program for one or more phases
4.12.2. Forcing options to a particular phase
4.12.3. Options affecting the C pre-processor
4.12.3.1. CPP and string gaps
4.12.4. Options affecting a Haskell pre-processor
4.12.5. Options affecting code generation
4.12.6. Options affecting linking
4.13. Using shared libraries
4.13.1. Building programs that use shared libraries
4.13.2. Shared libraries for Haskell packages
4.13.3. Shared libraries that export a C API
4.13.4. Finding shared libraries at runtime
4.13.4.1. Unix
4.13.4.2. Mac OS X
4.14. Using Concurrent Haskell
4.15. Using SMP parallelism
4.15.1. Compile-time options for SMP parallelism
4.15.2. RTS options for SMP parallelism
4.15.3. Hints for using SMP parallelism
4.16. Platform-specific Flags
4.17. Running a compiled program
4.17.1. Setting RTS options
4.17.1.1. Setting RTS options on the command line
4.17.1.2. Setting RTS options at compile time
4.17.1.3. Setting RTS options with the GHCRTS environment variable
4.17.1.4. “Hooks” to change RTS behaviour
4.17.2. Miscellaneous RTS options
4.17.3. RTS options to control the garbage collector
4.17.4. RTS options for concurrency and parallelism
4.17.5. RTS options for profiling
4.17.6. Tracing
4.17.7. RTS options for hackers, debuggers, and over-interested souls
4.17.8. Getting information about the RTS
4.18. Generating and compiling External Core Files
4.19. Debugging the compiler
4.19.1. Dumping out compiler intermediate structures
4.19.2. Formatting dumps
4.19.3. Suppressing unwanted information
4.19.4. Checking for consistency
4.19.5. How to read Core syntax (from some -ddump flags)
4.20. Flag reference
4.20.1. Help and verbosity options
4.20.2. Which phases to run
4.20.3. Alternative modes of operation
4.20.4. Redirecting output
4.20.5. Keeping intermediate files
4.20.6. Temporary files
4.20.7. Finding imports
4.20.8. Interface file options
4.20.9. Recompilation checking
4.20.10. Interactive-mode options
4.20.11. Packages
4.20.12. Language options
4.20.13. Warnings
4.20.14. Optimisation levels
4.20.15. Individual optimisations
4.20.16. Profiling options
4.20.17. Program coverage options
4.20.18. Haskell pre-processor options
4.20.19. C pre-processor options
4.20.20. Code generation options
4.20.21. Linking options
4.20.22. Plugin options
4.20.23. Replacing phases
4.20.24. Forcing options to particular phases
4.20.25. Platform-specific options
4.20.26. External core file options
4.20.27. Compiler debugging options
4.20.28. Misc compiler options
5. Profiling
5.1. Cost centres and cost-centre stacks
5.1.1. Inserting cost centres by hand
5.1.2. Rules for attributing costs
5.2. Compiler options for profiling
5.3. Time and allocation profiling
5.4. Profiling memory usage
5.4.1. RTS options for heap profiling
5.4.2. Retainer Profiling
5.4.2.1. Hints for using retainer profiling
5.4.3. Biographical Profiling
5.4.4. Actual memory residency
5.5. hp2ps––heap profile to PostScript
5.5.1. Manipulating the hp file
5.5.2. Zooming in on regions of your profile
5.5.3. Viewing the heap profile of a running program
5.5.4. Viewing a heap profile in real time
5.6. Profiling Parallel and Concurrent Programs
5.7. Observing Code Coverage
5.7.1. A small example: Reciprocation
5.7.2. Options for instrumenting code for coverage
5.7.3. The hpc toolkit
5.7.3.1. hpc report
5.7.3.2. hpc markup
5.7.3.3. hpc sum
5.7.3.4. hpc combine
5.7.3.5. hpc map
5.7.3.6. hpc overlay and hpc draft
5.7.4. Caveats and Shortcomings of Haskell Program Coverage
5.8. Using “ticky-ticky” profiling (for implementors)
6. Advice on: sooner, faster, smaller, thriftier
6.1. Sooner: producing a program more quickly
6.2. Faster: producing a program that runs quicker
6.3. Smaller: producing a program that is smaller
6.4. Thriftier: producing a program that gobbles less heap space
7. GHC Language Features
7.1. Language options
7.2. Unboxed types and primitive operations
7.2.1. Unboxed types
7.2.2. Unboxed tuples
7.3. Syntactic extensions
7.3.1. Unicode syntax
7.3.2. The magic hash
7.3.3. Hierarchical Modules
7.3.4. Pattern guards
7.3.5. View patterns
7.3.6. n+k patterns
7.3.7. Traditional record syntax
7.3.8. The recursive do-notation
7.3.8.1. Recursive binding groups
7.3.8.2. The mdo notation
7.3.9. Parallel List Comprehensions
7.3.10. Generalised (SQL-Like) List Comprehensions
7.3.11. Monad comprehensions
7.3.12. Rebindable syntax and the implicit Prelude import
7.3.13. Postfix operators
7.3.14. Tuple sections
7.3.15. Lambda-case
7.3.16. Multi-way if-expressions
7.3.17. Record field disambiguation
7.3.18. Record puns
7.3.19. Record wildcards
7.3.20. Local Fixity Declarations
7.3.21. Package-qualified imports
7.3.22. Safe imports
7.3.23. Summary of stolen syntax
7.4. Extensions to data types and type synonyms
7.4.1. Data types with no constructors
7.4.2. Data type contexts
7.4.3. Infix type constructors, classes, and type variables
7.4.4. Liberalised type synonyms
7.4.5. Existentially quantified data constructors
7.4.5.1. Why existential?
7.4.5.2. Existentials and type classes
7.4.5.3. Record Constructors
7.4.5.4. Restrictions
7.4.6. Declaring data types with explicit constructor signatures
7.4.7. Generalised Algebraic Data Types (GADTs)
7.5. Extensions to the "deriving" mechanism
7.5.1. Inferred context for deriving clauses
7.5.2. Stand-alone deriving declarations
7.5.3. Deriving clause for extra classes (Typeable, Data, etc)
7.5.4. Generalised derived instances for newtypes
7.5.4.1. Generalising the deriving clause
7.5.4.2. A more precise specification
7.6. Class and instances declarations
7.6.1. Class declarations
7.6.1.1. Multi-parameter type classes
7.6.1.2. The superclasses of a class declaration
7.6.1.3. Class method types
7.6.1.4. Default method signatures
7.6.2. Functional dependencies
7.6.2.1. Rules for functional dependencies
7.6.2.2. Background on functional dependencies
7.6.3. Instance declarations
7.6.3.1. Relaxed rules for the instance head
7.6.3.2. Relaxed rules for instance contexts
7.6.3.3. Undecidable instances
7.6.3.4. Overlapping instances
7.6.3.5. Type signatures in instance declarations
7.6.4. Overloaded string literals
7.7. Type families
7.7.1. Data families
7.7.1.1. Data family declarations
7.7.1.2. Data instance declarations
7.7.1.3. Overlap of data instances
7.7.2. Synonym families
7.7.2.1. Type family declarations
7.7.2.2. Type instance declarations
7.7.2.3. Overlap of type synonym instances
7.7.2.4. Decidability of type synonym instances
7.7.3. Associated data and type families
7.7.3.1. Associated instances
7.7.3.2. Associated type synonym defaults
7.7.3.3. Scoping of class parameters
7.7.4. Import and export
7.7.4.1. Examples
7.7.4.2. Instances
7.7.5. Type families and instance declarations
7.8. Kind polymorphism
7.8.1. Overview of kind polymorphism
7.8.2. Overview
7.8.3. Polymorphic kind recursion and complete kind signatures
7.9. Datatype promotion
7.9.1. Motivation
7.9.2. Overview
7.9.3. Distinguishing between types and constructors
7.9.4. Promoted lists and tuples types
7.9.5. Promoted Literals
7.10. Equality constraints
7.11. The Constraint kind
7.12. Other type system extensions
7.12.1. Explicit universal quantification (forall)
7.12.2. The context of a type signature
7.12.3. Implicit parameters
7.12.3.1. Implicit-parameter type constraints
7.12.3.2. Implicit-parameter bindings
7.12.3.3. Implicit parameters and polymorphic recursion
7.12.3.4. Implicit parameters and monomorphism
7.12.4. Explicitly-kinded quantification
7.12.5. Arbitrary-rank polymorphism
7.12.5.1. Examples
7.12.5.2. Type inference
7.12.5.3. Implicit quantification
7.12.6. Impredicative polymorphism
7.12.7. Lexically scoped type variables
7.12.7.1. Overview
7.12.7.2. Declaration type signatures
7.12.7.3. Expression type signatures
7.12.7.4. Pattern type signatures
7.12.7.5. Class and instance declarations
7.12.8. Generalised typing of mutually recursive bindings
7.12.9. Monomorphic local bindings
7.13. Deferring type errors to runtime
7.13.1. Enabling deferring of type errors
7.13.2. Deferred type errors in GHCi
7.14. Template Haskell
7.14.1. Syntax
7.14.2. Using Template Haskell
7.14.3. A Template Haskell Worked Example
7.14.4. Using Template Haskell with Profiling
7.14.5. Template Haskell Quasi-quotation
7.15. Arrow notation
7.15.1. do-notation for commands
7.15.2. Conditional commands
7.15.3. Defining your own control structures
7.15.4. Primitive constructs
7.15.5. Differences with the paper
7.15.6. Portability
7.16. Bang patterns
7.16.1. Informal description of bang patterns
7.16.2. Syntax and semantics
7.17. Assertions
7.18. Pragmas
7.18.1. LANGUAGE pragma
7.18.2. OPTIONS_GHC pragma
7.18.3. INCLUDE pragma
7.18.4. WARNING and DEPRECATED pragmas
7.18.5. INLINE and NOINLINE pragmas
7.18.5.1. INLINE pragma
7.18.5.2. INLINABLE pragma
7.18.5.3. NOINLINE pragma
7.18.5.4. CONLIKE modifier
7.18.5.5. Phase control
7.18.6. LINE pragma
7.18.7. RULES pragma
7.18.8. SPECIALIZE pragma
7.18.8.1. SPECIALIZE INLINE
7.18.8.2. SPECIALIZE for imported functions
7.18.8.3. Obsolete SPECIALIZE syntax
7.18.9. SPECIALIZE instance pragma
7.18.10. UNPACK pragma
7.18.11. NOUNPACK pragma
7.18.12. SOURCE pragma
7.19. Rewrite rules
7.19.1. Syntax
7.19.2. Semantics
7.19.3. How rules interact with INLINE/NOINLINE and CONLIKE pragmas
7.19.4. List fusion
7.19.5. Specialisation
7.19.6. Controlling what's going on in rewrite rules
7.19.7. CORE pragma
7.20. Special built-in functions
7.21. Generic classes
7.22. Generic programming
7.22.1. Deriving representations
7.22.2. Writing generic functions
7.22.3. Generic defaults
7.22.4. More information
7.23. Control over monomorphism
7.23.1. Switching off the dreaded Monomorphism Restriction
7.23.2. Monomorphic pattern bindings
7.24. Concurrent and Parallel Haskell
7.24.1. Concurrent Haskell
7.24.2. Software Transactional Memory
7.24.3. Parallel Haskell
7.24.4. Annotating pure code for parallelism
7.24.5. Data Parallel Haskell
7.25. Safe Haskell
7.25.1. Uses of Safe Haskell
7.25.1.1. Strict type-safety (good style)
7.25.1.2. Building secure systems (restricted IO Monads)
7.25.2. Safe Language
7.25.3. Safe Imports
7.25.4. Trust and Safe Haskell Modes
7.25.4.1. Trust check (-fpackage-trust disabled)
7.25.4.2. Trust check (-fpackage-trust enabled)
7.25.4.3. Example
7.25.4.4. Trustworthy Requirements
7.25.4.5. Package Trust
7.25.5. Safe Haskell Inference
7.25.6. Safe Haskell Flag Summary
8. Foreign function interface (FFI)
8.1. GHC extensions to the FFI Addendum
8.1.1. Unboxed types
8.1.2. Newtype wrapping of the IO monad
8.1.3. Primitive imports
8.1.4. Interruptible foreign calls
8.1.5. The CAPI calling convention
8.2. Using the FFI with GHC
8.2.1. Using foreign export and foreign import ccall "wrapper" with GHC
8.2.1.1. Using your own main()
8.2.1.2. Making a Haskell library that can be called from foreign code
8.2.2. Using header files
8.2.3. Memory Allocation
8.2.4. Multi-threading and the FFI
8.2.4.1. Foreign imports and multi-threading
8.2.4.2. The relationship between Haskell threads and OS threads
8.2.4.3. Foreign exports and multi-threading
8.2.4.4. On the use of hs_exit()
8.2.5. Floating point and the FFI
9. Extending and using GHC as a Library
9.1. Source annotations
9.1.1. Annotating values
9.1.2. Annotating types
9.1.3. Annotating modules
9.2. Using GHC as a Library
9.3. Compiler Plugins
9.3.1. Using compiler plugins
9.3.2. Writing compiler plugins
9.3.2.1. CoreToDo in more detail
9.3.2.2. Manipulating bindings
9.3.2.3. Using Annotations
10. An External Representation for the GHC Core Language (For GHC 6.10)
10.1. Introduction
10.2. External Grammar of Core
10.3. Informal Semantics
10.3.1. Program Organization and Modules
10.3.2. Namespaces
10.3.3. Types and Kinds
10.3.3.1. Types
10.3.3.2. Coercions
10.3.3.3. Kinds
10.3.3.4. Lifted and Unlifted Types
10.3.3.5. Type Constructors; Base Kinds and Higher Kinds
10.3.3.6. Type Synonyms and Type Equivalence
10.3.4. Algebraic data types
10.3.5. Newtypes
10.3.6. Expression Forms
10.3.7. Expression Evaluation
10.4. Primitive Module
10.4.1. Non-concurrent Back End
10.4.2. Literals
11. What to do when something goes wrong
11.1. When the compiler “does the wrong thing”
11.2. When your program “does the wrong thing”
12. Other Haskell utility programs
12.1. “Yacc for Haskell”: happy
12.2. Writing Haskell interfaces to C code: hsc2hs
12.2.1. command line syntax
12.2.2. Input syntax
12.2.3. Custom constructs
12.2.4. Cross-compilation
13. Running GHC on Win32 systems
13.1. Starting GHC on Windows platforms
13.2. Running GHCi on Windows
13.3. Interacting with the terminal
13.4. Differences in library behaviour
13.5. Using GHC (and other GHC-compiled executables) with cygwin
13.5.1. Background
13.5.2. The problem
13.5.3. Things to do
13.6. Building and using Win32 DLLs
13.6.1. Creating a DLL
13.6.2. Making DLLs to be called from other languages
13.6.2.1. Using from VBA
13.6.2.2. Using from C++
14. Known bugs and infelicities
14.1. Haskell standards vs. Glasgow Haskell: language non-compliance
14.1.1. Divergence from Haskell 98 and Haskell 2010
14.1.1.1. Lexical syntax
14.1.1.2. Context-free syntax
14.1.1.3. Expressions and patterns
14.1.1.4. Declarations and bindings
14.1.1.5. Module system and interface files
14.1.1.6. Numbers, basic types, and built-in classes
14.1.1.7. In Prelude support
14.1.1.8. The Foreign Function Interface
14.1.2. GHC's interpretation of undefined behaviour in Haskell 98 and Haskell 2010
14.2. Known bugs or infelicities
14.2.1. Bugs in GHC
14.2.2. Bugs in GHCi (the interactive GHC)
Index