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(?Column)

Width of a line. If the output is a tty and tty_size/2 can produce a size the default is the number of columns minus 8. Otherwise the default is 72 characters. If the Column is unbound it is unified with the computed value.

left_margin(+Integer)

Left margin for continuation lines. Default is the current line position or 0 if that is not available.

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. See also auto_indent_arguments(Int)

An integer

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

auto_indent_arguments(+Integer)

Used by indent_arguments(auto) to decide whether to introduce a newline after the `(` or not. If specified and > 0, this provides the default integer for indent_arguments(Int). The "hanging" mode is used if otherwise the indentation increment is twice this value.

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)
    ]

fullstop(Boolean)

If true (default false), add a full stop (.) to the output.

nl(Boolean)

If true (default false), add a newline to the output.