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improved things a little based on Eli's and Greg Woodhouse's comments

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svn: r11384
This commit is contained in:
Robby Findler 2008-08-22 14:13:12 +00:00
parent 979766bee5
commit de74567f46
1 changed files with 25 additions and 6 deletions
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31
collects/scribblings/guide/contracts-simple-function.scrbl
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@ -227,7 +227,8 @@ scheme
(code:comment "convert a random number to a string")
[format-number (-> number? string?)]
(code:comment "convert an amount into a dollar based string")
(code:comment "convert an amount into a string with a decimal")
(code:comment "point, as in an amount of US currency")
[format-nat (-> natural-number/c
(and/c string? has-decimal?))])
]
@ -268,18 +269,36 @@ scheme
(provide/contract
...
(code:comment "convert a random number to a string")
(code:comment "convert a number to a string")
[format-number (-> number? string?)]
(code:comment "convert an amount (natural number) of cents")
(code:comment "into a dollar based string")
[format-nat (-> natural-number/c
(lambda (result)
(and (string? result)
(is-decimal-string? result))))])
(and/c string?
is-decimal-string?))])
]
@ctc-section{Contracts on Higher-order Functions}
Function contracts are not just restricted to having simple
predicates on their domains or ranges. Any of the contract
combinators discussed here, including function contracts
themselves, can be used as contracts on the arguments and
results of a function.
For example,
@schemeblock[(-> integer? (-> integer? integer?))]
is a contract that describes a curried function. It matches
functions that accept one argument and then return another
function accepting a second argument before finally
returning an integer.
This contract
@schemeblock[(-> (-> integer? integer?) integer?)]
describes functions that accept other functions as inputs.
@ctc-section{The Difference Between @scheme[any] and @scheme[any/c]}
The contract @scheme[any/c] accepts any value, and
@ -304,7 +323,7 @@ example, this function:
]
meets the first contract, but not the second one.}
@item{Relatedly, this means that a call to a function that
@item{This also means that a call to a function that
has the second contract is not a tail call. So, for example,
the following program is an infinite loop that takes only a constant
amount of space, but if you replace @scheme[any] with