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| author | Hugo Hörnquist <hugo@lysator.liu.se> | 2018-11-16 00:09:13 +0100 |
|---|---|---|
| committer | Hugo Hörnquist <hugo@lysator.liu.se> | 2018-11-16 00:09:13 +0100 |
| commit | 6269a1345996b96e2194a54c34028ab73d27a004 (patch) | |
| tree | 415b9f2741657aa0a9ea3efbad7eb8da6abc7cc5 | |
| parent | Add modify to (control monad state). (diff) | |
| download | scheme-monad-6269a1345996b96e2194a54c34028ab73d27a004.tar.gz scheme-monad-6269a1345996b96e2194a54c34028ab73d27a004.tar.xz | |
Add fmap instance for state monad.
| -rw-r--r-- | control/monad/state.scm | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/control/monad/state.scm b/control/monad/state.scm index 603e387..f7190af 100644 --- a/control/monad/state.scm +++ b/control/monad/state.scm @@ -2,8 +2,9 @@ #:use-module (oop goops) #:use-module (ice-9 match) #:use-module (control monad) - #:re-export (>>= >>)) - #:export (return-state run-state get put modify)) + #:use-module (data functor) + #:export (return-state run-state get put modify) + #:re-export (>>= >> fmap)) ;; Alternative implementation of get. @@ -71,7 +72,11 @@ ((r s) (list '() (proc s))))) +(define-stateful-method ((fmap (f <procedure>) (s <state>)) st-list) + (match ((proc s) st-list) + ((r st) + (list (f r) st)))) + (define-method (run-state (st <state>) init) "Exec state with init as starting state value and st." ((proc st) (list init init))) - |