1 PLAI Scheme
| #lang plai |
PLAI Scheme is derived from the scheme langauge. In addition, it includes the define-type and type-case forms and testing support.
1.1 Defining Types: define-type
| (define-type type-id variant ...) | |||||
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The value of each field is checked by its associated contract-expr. A contract-expr may be an arbitrary predicate or a contract.
In addition to the contructors, a define-type expression also defines:
a predicate type-id? that returns true for instances of the datatype, and false for any other value,
for each variant, a predicate variant-id? that returns true when applied to a value of the same variant and false for any other value,
for each field of each variant, an accessor variant-id-field-id that returns the value of the field, and
for each field of each variant, a mutator set-variant-id-field-id! that set the value of the field.
1.2 Deconstructing Data Structures: type-case
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If a branch is not specified for each variant, you may use an else branch to create a catch-all branch. An else branch must be the last branch in the sequence of branches. type-case signals a compile-time error if all variants are not covered and the else branch is missing. Similarly, type-case signals a compile-time error if an else branch is unreachable because a branch exists for all variants.
1.3 Testing Infrastructure
PLAI Scheme provides the following syntactic forms for testing.
| (test result-expr expected-expr) |
(good result-expr result-value expected-value location).
If they do not evaluate to the same value, the test prints
(bad result-expr result-value expected-value location).
If evaluating result-expr signals an error, the test prints
(exception result-expr exception-message <no-expected-value> location)
If evaluating expected-expr signals an error, the test prints
(pred-exception result-expr exception-message <no-expected-value> location)
| (test/pred result-expr pred?) |
If evaluating pred? signals an error, the test prints
(pred-exception result-expr exception-message <no-expected-value> location)
The syntax of pred? is considered expected-value for the purposes of test reporting.
| (test/exn result-expr error-message) |
For example, the following test succeeds:
(test/exn (error "/: division by zero") "by zero")
The error message is "/: division by zero", and "by zero" is a substring of the error message. However, the following test fails:
Although the expression raises an exception and the error string contains "by zero", since the error was not explicitly raised by user-written code, the test fails.
The evaluation of error-message is considered expected-value for the purposes of test reporting.
| (test/regexp result-expr error-message-regexp) |
The evaluation of error-message-regexp is considered expected-value for the purposes of test reporting.
1.3.1 Test Flags
| (abridged-test-output [abridge?]) → void? |
| abridge? : boolean? = false |
| (plai-catch-test-exn [catch?]) → void? |
| catch? : boolean? = true |
| (halt-on-errors [halt?]) → void? |
| halt? : boolean? = true |
| (print-only-errors [print?]) → void? |
| print? : boolean? = true |
| (test-inexact-epsilon epsilon) → void? |
| epsilon : number? |
| (plai-ignore-exn-strings ignore?) → void? |
| ignore? : boolean? |