Details
In Lucid (and other dataflow languages) an expression that contains a variable that was not yet bound waits until the variable is bound before proceeding. An expression like x + y will wait until both x and y are bound before returning with the output of the expression. An important result of this is that explicit logic for updating related values is avoided, which results in substantial code reduction compared to mainstream languages.
Each variable in Lucid is a stream of values. An expression n = 1 fby n + 1 defines a stream using the operator 'fby' (a mnemonic for "followed by"). fby defines what comes after the previous expression. (In this instance the stream produces 1,2,3,...). The values in a stream can be addressed by these operators (assuming x is the variable being used):
'first x' - fetches the first value in the stream x,
'x' - the current value of the stream,
'next x' - fetches the next value in the stream.
'asa' - an operator that does some thing 'as soon as' the condition given becomes true.
'x upon p' - upon is an operator that repeats the old value of the stream x, and updates to the new values only when the stream p makes a true value available. (It serves to slow down the stream x) i.e.: x upon p is the stream x with new values appearing upon the truth of p.
The computation is carried out by defining filters or transformation functions that act on these time-varying streams of data.
pLucid was the first interpreter for Lucid.
Read more about this topic: Lucid (programming Language)
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