22 Debugging tools

(require (planet untyped/unlib/debug))

Utilities for printing the runtime values of variables for debugging purposes, with minimal disruption to code structure.

(debug-enabled?) → boolean?

(debug-enabled? val) → void?

val : boolean?

Boolean parameter for enabling or disabling the printing of debugging information. Defaults to #t.

(current-debug-printer) → (-> string? any void?)

(current-debug-printer proc) → void?

proc : (-> string? any void?)

Parameter controlling the formatting of printed debugging information. Value must be a procedure that takes a message and a value and returns void. The default value prints the message and a colon on one line and pretty-prints the value (slightly indented) on subsequent lines.

(debug val) → any

val : any

Prints val and returns it transparently.

Examples:

> (length (debug "square"                    (for/list ([j '(1 2 3 4 5)])                      (for/list ([i '(1 2 3 4 5)])                        i))))

square:     ((1 2 3 4 5)      (1 2 3 4 5)      (1 2 3 4 5)      (1 2 3 4 5)      (1 2 3 4 5))

5

(debug* proc arg ...) → any

proc : procedure?

arg : any

Applies proc to args and prints and returns the return value transparently.

Examples:

> (add1 (debug* "message" * 2 2))

message:     4

5

(define-debug id expr)

Expands to a define form that prints the value of id as a side effect.

Examples:

> (define-debug test-data       (+ 1 2 3))

test-data:     6

(let-debug ([id expr] ...) expr ...)

Expands to a let form that prints the value of each id as it is assigned.

Examples:

> (let-debug ([a (+ 1 2)]                 [b (+ 3 4)])        (list a b))

a:     3   b:     7

(3 7)

(let*-debug ([id expr] ...) expr ...)

Expands to a let* form that prints the value of each id as it is assigned.

Examples:

> (let*-debug ([a (+ 1 2)]                  [b (* a a)])        (list a b))

a:     3   b:     9

(3 9)

(letrec-debug ([id expr] ...) expr ...)

Expands to a letrec form that prints the value of each id as it is assigned.

Examples:

> (letrec-debug ([a (+ 1 2)]                    [b (* a a)])        (list a b))

a:     3   b:     9

(3 9)

(with-pretty-indent prefix expr ...)

Parameterizes the pretty-print-print-line parameter to a procedure that acts the same as the default, except that every line is prefixed with prefix. prefix must be a string.

Examples:

> (define square       (for/list ([j '(1 2 3 4 5)])         (for/list ([i '(1 2 3 4 5)])           i)))

> (pretty-print square)

((1 2 3 4 5)    (1 2 3 4 5)    (1 2 3 4 5)    (1 2 3 4 5)    (1 2 3 4 5))

> (with-pretty-indent "..."       (pretty-print square))

...((1 2 3 4 5)   ... (1 2 3 4 5)   ... (1 2 3 4 5)   ... (1 2 3 4 5)   ... (1 2 3 4 5))

(exn-context exn) → (listof symbol?)

exn : exn?

Returns a printable form of the continuation marks of exn that can can be used with pretty-print to produce simple, legible debugging output.