pprint.pl -- Pretty Print Prolog terms

This module is a first start of what should become a full-featured pretty printer for Prolog terms with many options and parameters. Eventually, it should replace portray_clause/1 and various other special-purpose predicates.

To be done

- This is just a quicky. We need proper handling of portray/1, avoid printing very long terms multiple times, spacing (around operators), etc.

- Use a record for the option-processing.

- The current approach is far too simple, often resulting in illegal terms.

 print_term(+Term, +Options) is det

Pretty print a Prolog term. The following options are processed:

output(+Stream)

Define the output stream. Default is user_output

right_margin(+Integer)

Width of a line. Default is 72 characters.

left_margin(+Integer)

Left margin for continuation lines. Default is 0.

tab_width(+Integer)

Distance between tab-stops. Default is 8 characters.

indent_arguments(+Spec)

Defines how arguments of compound terms are placed. Defined values are:

false

Simply place them left to right (no line-breaks)

true

Place them vertically, aligned with the open bracket (not implemented)

auto (default)

As horizontal if line-width is not exceeded, vertical otherwise.

An integer

Place them vertically aligned, <N> spaces to the right of the beginning of the head.

operators(+Boolean)

This is the inverse of the write_term/3 option ignore_ops. Default is to respect them.

write_options(+List)

List of options passed to write_term/3 for terms that are not further processed. Default:

    [ numbervars(true),
      quoted(true),
      portray(true)
    ]

 prepare_term(+Term, -Template, -Cycles, -Constraints)[private]

Prepare a term, possibly holding cycles and constraints for printing.

 indent(+Out, +Indent, +Options)[private]

Newline and indent to the indicated column. Respects the option tab_width. Default is 8. If the tab-width equals zero, indentation is emitted using spaces.

 print_width(+Term, -W, +Options) is det[private]

Width required when printing `normally' left-to-right.

 pprint(+Term, +Context, +Options)[private]

The bottom-line print-routine.