Editing Functional Reactive Programming (section)

== History ==

=== A possible predecessor? ===

In his thesis [https://core.ac.uk/download/9835633.pdf Functional Real-Time Programming: The Language Ruth And Its Semantics], some parts of the semantics Dave Harrison gives for ''Ruth'' bears a curious resemblance to those for FRP:

* <small>(page 48)</small>
:{|
|<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
A channel is an infinite stream of timestamped data values, or messages, each message denoting an event in the system. [...]
</div>
<sup> </sup>
<haskell>
type Channel a = [Event a]
data Event a   = At Time a
</haskell>
|}

* <small>(page 61)</small>
:{|
|<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
In the semantics given in Chapter 5 every <i>Ruth</i> program is supplied with a tree of time values (or clock) as suggested in [https://academic.oup.com/comjnl/article-pdf/31/3/243/1157325/310243.pdf this paper] and each <i>Ruth</i> process is given a different sub-tree of the clock [...]
</div>
<sup> </sup>
<haskell>
type Program = Clock -> ...
type Process a = Clock -> a

type Clock = Tree Time
left  :: Clock -> Clock
right :: Clock -> Clock
</haskell>
<sup> </sup>
<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
A clock tree is composed of a node holding a non-negative integer denoting the current time and two sub-trees containing the times of future events. As the tree is (lazily) evaluated each of the nodes is instantiated with the value of system time <i>at the time at which the node is instantiated</i>, thus giving programs reference to the current time. [...]
</div>
<sup> </sup>
<haskell>
type Time   = Integer  -- must be zero or larger 
data Tree a = Node { contents :: a,
                     left     :: Tree a,
                     right    :: Tree a }

currentTime :: Clock -> Time
currentTime = contents
</haskell>
|}

Regarding Harrison's semantics:
<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote"><small>(page 53)</small>

The semantics of <i>Ruth</i> given in Chapter 5 assume a normal order evaluation strategy such as is provided by the technique of lazy evaluation [...]. Consequently <code>whererec</code> can be used to define infinite data structures.
</div>

[[Category:FRP|*]]