Converted Printing: pconver.ss

This library defines routines for printing Scheme values as evaluatable S-expressions rather than readable S-expressions. The print-convert procedure does not print values; rather, it converts a Scheme value into another Scheme value such that the new value pretty-prints as a Scheme expression that evaluates to the original value. For example, (pretty-print (print-convert `(9 ,(box 5) #(6 7))) prints the literal expression (list 9 (box 5) (vector 6 7)) to the current output port.

To install print converting into the read-eval-print loop, require pconver.ss and call the procedure install-converting-printer.

In addition to print-convert, this library provides print-convert, build-share, get-shared, and print-convert-expr. The last three are used to convert sub-expressions of a larger expression (potentially with shared structure).

Parameter that controls how lists are represented with constructor-style conversion. If the parameter's value is #t, lists are represented using list. Otherwise, lists are represented using cons. The initial value of the parameter is #t.

Parameter that controls how #t and #f are represented. If the parameter's value is #t, then #t is represented as true and #f is represented as false. The initial value of the parameter is #t.

Takes a value and computes sharing information used for representing the value as an expression. The return value is an opaque structure that can be passed back into get-shared or print-convert-expr.

Parameter that controls how values are represented after conversion. If this parameter is #t, then constructors are used, e.g., pair containing 1 and 2 is represented as (cons 1 2). Otherwise, quasiquote-style syntax is used, e.g. the pair containing 1 and 2 is represented as `(1 . 2). The initial value of the parameter is #f.

See also quasi-read-style-printing.

Parameter that sets a procedure used by print-convert and build-share to assemble sharing information. The procedure hook takes three arguments: a value v, a procedure basic-share, and a procedure sub-share; the return value is ignored. The basic-share procedure takes v and performs the built-in sharing analysis, while the sub-share procedure takes a component of v ands analyzes it. These procedures return void; sharing information is accumulated as values are passed to basic-share and sub-share.

A current-build-share-hook procedure usually works together with a current-print-convert-hook procedure.

Parameter that sets a procedure used by print-convert and build-share to generate a new name for a shared value. The hook procedure takes a single value and returns a symbol for the value's name. If hook returns #f, a name is generated using the form ``-n-'' (where n is an integer).

Parameter that sets a procedure used by print-convert and print-convert-expr to convert values. The procedure hook takes three arguments -- a value v, a procedure basic-convert, and a procedure sub-convert -- and returns the converted representation of v. The basic-convert procedure takes v and returns the default conversion, while the sub-convert procedure takes a component of v and returns its conversion.

A current-print-convert-hook procedure usually works together with a current-build-share-hook procedure.

Parameter that sets the prompt used by install-converting-printer. The initial value is "|- ".

The shared-info value must be a result from build-share. The procedure returns a list matching variables to shared values within the value passed to build-share. For example,

  (get-shared (build-share (shared ([a (cons 1 b)][b (cons 2 a)]) a))) 

  ((-1- (cons 1 -2-)) (-2- (cons 2 -1-))) 

Sets the current print handler to print values using print-convert. The current read handler is also set to use the prompt returned by current-read-eval-convert-print-prompt.

Converts the value v. If cycles-only? is not #f, then only circular objects are included in the output. The default value of cycles-only? is the value of (show-sharing).

Converts the value v using sharing information share-info previously returned by build-share for a value containing v. If the most recent call to get-shared with share-info requested information only for cycles, then print-convert-expr will only display sharing among values for cycles, rather than showing all value sharing.

The unroll-once? argument is used if v is a shared value in share-info. In this case, if unroll-once? is #f, then the return value will be a shared-value identifier; otherwise, the returned value shows the internal structure of v (using shared value identifiers within v's immediate structure as appropriate).

Parameter that controls how vectors and boxes are represented after conversion when the value of constructor-style-printing is #f. If quasi-read-style-printing is set to #f, then boxes and vectors are unquoted and represented using constructors. For example, the list of a box containing the number 1 and a vector containing the number 1 is represented as `(,(box 1) ,(vector 1)). If the parameter is #t, then #& and #() are used, e.g., `(#&1 #(1)). The initial value of the parameter is #t.

Parameter that determines whether sub-value sharing is conserved (and shown) in the converted output by default. The initial value of the parameter is #t.

Parameter that controls how exact, non-integer numbers are converted when the numerator is greater than the denominator. If the parameter's value is #t, the number is converted to the form (+ integer fraction) (i.e., a list containing '+, an exact integer, and an exact rational less than 1 and greater than -1). The initial value of the parameter is #t.