Maintainer | Ralf Laemmel, Joost Visser |
---|---|

Stability | experimental |

Portability | portable |

Safe Haskell | None |

Language | Haskell98 |

- Try: recover from failure
- Test: ignore result, but retain effects
- If-then-else: pass value from condition to then-clause
- If-then: disciplined form of a guarding
- Not: negation by failure
- Exclusive choice
- Generic filter, derived from monomorphic predicate
- Generic ticker, derived from monomorphic predicate
- Type guards
- Generic ticker, derived from type guard
- Generic filters, derived from type guard

This module is part of `StrategyLib`

, a library of functional strategy
combinators, including combinators for generic traversal. This module
defines combinators to wire up control and data flow. Whenever possible,
we define the combinators in an overloaded fashion but we provide
type-specialised variants for TP and TU for convenience.

- tryS :: (StrategyPlus s m, StrategyMonoid s m) => s m -> s m
- tryTP :: MonadPlus m => TP m -> TP m
- tryTU :: (MonadPlus m, Monoid u) => TU u m -> TU u m
- testS :: Strategy s m => s m -> TP m
- testTP :: Monad m => TP m -> TP m
- testTU :: Monad m => TU a m -> TP m
- ifS :: StrategyPlus s m => TU u m -> (u -> s m) -> s m -> s m
- ifTP :: MonadPlus m => TU u m -> (u -> TP m) -> TP m -> TP m
- ifTU :: MonadPlus m => TU u m -> (u -> TU u' m) -> TU u' m -> TU u' m
- ifthenS :: Strategy s m => TU () m -> s m -> s m
- ifthenTP :: Monad m => TU () m -> TP m -> TP m
- ifthenTU :: Monad m => TU () m -> TU u m -> TU u m
- notS :: StrategyPlus s m => s m -> TP m
- notTP :: MonadPlus m => TP m -> TP m
- notTU :: MonadPlus m => TU u m -> TP m
- xchoiceS :: StrategyPlus s m => s m -> s m -> s m
- xchoiceTP :: MonadPlus m => TP m -> TP m -> TP m
- xchoiceTU :: MonadPlus m => TU u m -> TU u m -> TU u m
- filterTP :: (Term t, MonadPlus m) => (t -> Bool) -> TP m
- filterTU :: (Term t, MonadPlus m) => (t -> Bool) -> TU t m
- tickTU :: (Monad m, Term t, Num n) => (t -> Bool) -> TU n m
- type TypeGuard a = a -> ()
- typeGuard :: TypeGuard a
- typeTickTU :: (Term t, Monad m, Num n) => TypeGuard t -> TU n m
- typeFilterTP :: (Term t, MonadPlus m) => TypeGuard t -> TP m
- typeFilterTU :: (Term t, MonadPlus m) => TypeGuard t -> TU t m

# Try: recover from failure

tryS :: (StrategyPlus s m, StrategyMonoid s m) => s m -> s m Source

Attempt a strategy `s`

, but recover if it fails.

tryTP :: MonadPlus m => TP m -> TP m Source

Attempt a type-preserving strategy `s`

, but if it fails, return the
input term unchanged.

# Test: ignore result, but retain effects

testS :: Strategy s m => s m -> TP m Source

Test for a strategy's success in a type-preserving context.

testTP :: Monad m => TP m -> TP m Source

Test for a type-preserving strategy's success in a type-preserving context.

testTU :: Monad m => TU a m -> TP m Source

Test for a type-unifying strategy's success in a type-preserving context.

# If-then-else: pass value from condition to then-clause

ifS :: StrategyPlus s m => TU u m -> (u -> s m) -> s m -> s m Source

If `c`

succeeds, pass its value to the then-clause `t`

,
otherwise revert to the else-clause `e`

.

ifTP :: MonadPlus m => TU u m -> (u -> TP m) -> TP m -> TP m Source

If `c`

succeeds, pass its value to the then-clause `t`

,
otherwise revert to the else-clause `e`

.

ifTU :: MonadPlus m => TU u m -> (u -> TU u' m) -> TU u' m -> TU u' m Source

If `c`

succeeds, pass its value to the then-clause `t`

,
otherwise revert to the else-clause `e`

.

# If-then: disciplined form of a guarding

ifthenS :: Strategy s m => TU () m -> s m -> s m Source

Guard then-clause `t`

by the void-valued type-unifying
condition `c`

.

ifthenTP :: Monad m => TU () m -> TP m -> TP m Source

Guard type-preserving then-clause `t`

by the void-valued type-unifying
condition `c`

.

ifthenTU :: Monad m => TU () m -> TU u m -> TU u m Source

Guard type-unifying then-clause `t`

by the void-valued type-unifying
condition `c`

.

# Not: negation by failure

notS :: StrategyPlus s m => s m -> TP m Source

Invert the success-value of strategy `s`

.

notTP :: MonadPlus m => TP m -> TP m Source

Invert the success-value of type-preserving strategy `s`

. Its output
term (in case of success) will be ignored.

notTU :: MonadPlus m => TU u m -> TP m Source

Invert the success-value of type-unifying strategy `s`

. Its output
value (in case of success) will be ignored.

# Exclusive choice

xchoiceS :: StrategyPlus s m => s m -> s m -> s m Source

Succeed if exactly one argument strategy succeeds.

xchoiceTP :: MonadPlus m => TP m -> TP m -> TP m Source

Succeed if exactly one argument strategy succeeds.

xchoiceTU :: MonadPlus m => TU u m -> TU u m -> TU u m Source

Succeed if exactly one argument strategy succeeds.

# Generic filter, derived from monomorphic predicate

filterTP :: (Term t, MonadPlus m) => (t -> Bool) -> TP m Source

If predicate `g`

holds for the input term, return it as output term,
otherwise fail.

filterTU :: (Term t, MonadPlus m) => (t -> Bool) -> TU t m Source

If predicate `g`

holds for the input term, return it as output value,
otherwise fail.

# Generic ticker, derived from monomorphic predicate

tickTU :: (Monad m, Term t, Num n) => (t -> Bool) -> TU n m Source

If predicate `g`

holds for the input term,
return 1 otherwise return 0.

# Type guards

type TypeGuard a = a -> () Source

Type guard (function type), i.e., guard that does not observe values

typeGuard :: TypeGuard a Source

Type guard (function). Typical usage:

full_tdTU (typeTickTU (typeGuard::TypeGuard MyType))

# Generic ticker, derived from type guard

typeTickTU :: (Term t, Monad m, Num n) => TypeGuard t -> TU n m Source

If type guard holds for the input term, return 1 otherwise return 0.