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contract docs: explain positive and negative as server and client

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Alex Knauth 2015-05-15 20:20:08 -04:00 committed by Robby Findler
parent a9ac3be43c
commit d30b90cba3
1 changed files with 12 additions and 9 deletions
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21
pkgs/racket-doc/scribblings/guide/contracts/new-combinators.scrbl
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@ -67,13 +67,13 @@ The new argument specifies who is to be blamed for
positive and negative contract violations.
Contracts, in this system, are always
established between two parties. One party provides some
value according to the contract, and the other consumes the
value, also according to the contract. The first is called
the ``positive'' person and the second the ``negative''. So,
established between two parties. One party, the "server," provides some
value according to the contract, and the other, the "client," consumes the
value, also according to the contract. The "server" is called
the ``positive'' person and the "client" the ``negative''. So,
in the case of just the integer contract, the only thing
that can go wrong is that the value provided is not an
integer. Thus, only the positive party can ever accrue
integer. Thus, only the positive party (the "server") can ever accrue
blame. The @racket[raise-blame-error] function always blames
the positive party.
@ -114,16 +114,19 @@ This technique is not merely a cheap trick to get the example to work,
however. The reversal of the positive and the negative is a
natural consequence of the way functions behave. That is,
imagine the flow of values in a program between two
modules. First, one module defines a function, and then that
module is required by another. So far, the function itself
modules. First, one module (the "server") defines a function, and then that
module is required by another (the "client"). So far, the function itself
has to go from the original, providing module to the
requiring module. Now, imagine that the providing module
invokes the function, supplying it an argument. At this
point, the flow of values reverses. The argument is
traveling back from the requiring module to the providing
module! And finally, when the function produces a result,
module! The "client" is "serving" the argument to the "server,"
and the "server" is recieving that value as a "client."
And finally, when the function produces a result,
that result flows back in the original
direction. Accordingly, the contract on the domain reverses
direction from "server" to "client."
Accordingly, the contract on the domain reverses
the positive and the negative blame parties, just like the flow
of values reverses.