diff options
| -rw-r--r-- | sly/signal.scm | 46 |
1 files changed, 32 insertions, 14 deletions
diff --git a/sly/signal.scm b/sly/signal.scm index 3f5972f..9dafff6 100644 --- a/sly/signal.scm +++ b/sly/signal.scm @@ -31,6 +31,7 @@ #:export (signal? make-signal define-signal + signal unsignal signal-let signal-let* hook->signal add-signal-hook! @@ -138,9 +139,20 @@ SIGNAL." SIGNAL-BOX-IN changes, the value will be propagated to SIGNAL-OUT." (hashq-set! (signal-outputs (signal-unbox signal-box-in)) signal-out #f)) +(define signal-graph-access? (make-parameter #t)) + +(define-syntax-rule (without-signal-graph-access body ...) + "Evaluate BODY but throw an error if it attempts to apply 'signal-ref' +or 'signal-set!'. Protecting the signal graph in this way is intended +to catch common newbie mistakes where impurities are introduced in +procedures that are meant to be pure." + (parameterize ((signal-graph-access? #f)) body ...)) + (define (signal-ref signal) "Return the value stored within SIGNAL." - (%signal-ref (signal-unbox signal))) + (if (signal-graph-access?) + (%signal-ref (signal-unbox signal)) + (error "Use of signal-ref is not allowed when computing the value of a signal"))) (define (signal-ref-maybe object) "Return the value stored within OBJECT if OBJECT is a signal. @@ -168,6 +180,8 @@ all output signals." "Change the contents of SIGNAL to VALUE. This procedure should almost never be used, except to bootstrap a root node of a signal graph." + (unless (signal-graph-access?) + (error "Use of signal-set! is not allowed when computing the value of a signal")) (%signal-set! (signal-unbox signal) value)) (define (splice-signals! to from) @@ -186,6 +200,17 @@ already a signal." value (make-signal value))) +(define-syntax signal + (syntax-rules (unsignal) + ((_ (unsignal arg ...)) + (begin arg ...)) + ((_ (proc arg ...)) + (if (signal? proc) + (signal-call proc (signal arg) ...) + (signal-map proc (signal arg) ...))) + ((_ value) + (make-signal-maybe value)))) + (define-syntax define-signal (lambda (x) "Create a top-level signal variable. If the named variable @@ -193,26 +218,16 @@ already exists and has a signal value then its outputs will be spliced into the new signal. If the given value is not a signal then it will be coerced into one." (syntax-case x () - ((_ name (signal ...)) - (defined? (syntax->datum #'name)) - #'(let ((s (make-signal-maybe (signal ...)))) - (if (signal? name) - (begin - (splice-signals! name s) - (signal-propagate! (signal-unbox name))) - (set! name s)))) ((_ name value) (defined? (syntax->datum #'name)) - #'(let ((s (make-signal-maybe value))) + #'(let ((s (signal value))) (if (signal? name) (begin (splice-signals! name s) (signal-propagate! (signal-unbox name))) (set! name s)))) - ((_ name (signal ...)) - #'(define name (make-signal-maybe (signal ...)))) ((_ name value) - #'(define name (make-signal-maybe value)))))) + #'(define name (signal value)))))) ;; emacs: (put 'signal-let 'scheme-indent-function 1) @@ -268,7 +283,10 @@ SIGNALS." or more SIGNALs." (let ((inputs (cons signal rest))) (define (current-value) - (apply proc (map signal-ref inputs))) + (let ((args (map signal-ref inputs))) + (without-signal-graph-access + (apply proc args)))) + (make-boxed-signal (current-value) (lambda (self value) (%signal-set! self (current-value))) |