Source code for ufl.precedence

"""Precedence handling."""

# Copyright (C) 2008-2016 Martin Sandve Alnæs
#
# This file is part of UFL (https://www.fenicsproject.org)
#
# SPDX-License-Identifier:    LGPL-3.0-or-later

import warnings

# FIXME: This code is crap...


def parstr(child, parent, pre="(", post=")", format=str):
    """Parstr."""
    # Execute when needed instead of on import, which leads to all
    # kinds of circular trouble.  Fixing this could be an optimization
    # of str(expr) though.
    if not hasattr(parent, "_precedence"):
        assign_precedences(build_precedence_list())

    # We want child to be evaluated fully first, and if the parent has
    # higher precedence we later wrap in ().
    s = format(child)

    # Operators where operands are always parenthesized because
    # precedence is not defined below
    if parent._precedence == 0:
        return pre + s + post

    # If parent operator binds stronger than child, must parenthesize
    # child
    # FIXME: Is this correct for all possible positions of () in a + b + c?
    # FIXME: Left-right rule
    if parent._precedence > child._precedence:  # parent = indexed, child = terminal
        return pre + s + post

    # Nothing needed
    return s


def build_precedence_list():
    """Build precedence list."""
    from ufl.classes import (
        Abs,
        BesselFunction,
        Division,
        Indexed,
        IndexSum,
        MathFunction,
        Operator,
        Power,
        Product,
        Sum,
        Terminal,
    )

    # TODO: Fill in other types...
    # Power <= Transposed

    precedence_list = []
    # Default operator behaviour: should always add parentheses
    precedence_list.append((Operator,))

    precedence_list.append((Sum,))

    # sum_i a + b = (sum_i a) + b != sum_i (a + b), sum_i binds
    # stronger than +, but weaker than product
    precedence_list.append((IndexSum,))

    precedence_list.append(
        (
            Product,
            Division,
        )
    )

    # NB! Depends on language!
    precedence_list.append((Power, MathFunction, BesselFunction, Abs))

    precedence_list.append((Indexed,))

    # Default terminal behaviour: should never add parentheses
    precedence_list.append((Terminal,))
    return precedence_list


def build_precedence_mapping(precedence_list):
    """Given a precedence list, build a dict with class->int mappings.

    Utility function used by some external code.
    """
    from ufl.classes import Expr, abstract_classes, all_ufl_classes

    pm = {}
    missing = set()
    # Assign integer values for each precedence level
    k = 0
    for p in precedence_list:
        for c in p:
            pm[c] = k
        k += 1
    # Check for missing classes, fill in subclasses
    for c in all_ufl_classes:
        if c not in abstract_classes and c not in pm:
            b = c.__bases__[0]
            while b is not Expr:
                if b in pm:
                    pm[c] = pm[b]
                    break
                b = b.__bases__[0]
            if c not in pm:
                missing.add(c)
    return pm, missing


def assign_precedences(precedence_list):
    """Given a precedence list, assign ints to class._precedence."""
    pm, missing = build_precedence_mapping(precedence_list)
    for c, p in sorted(pm.items(), key=lambda x: x[0].__name__):
        c._precedence = p
    if missing:
        warnings.warn(
            "Missing precedence levels for classes:\n"
            + "\n".join(f"  {c}" for c in sorted(missing))
        )