Input and output¶

Python streams (io.StringIO, files, sys.stdout, ...) are accepted wherever logic code reads or writes: by parsers, and by solvers' input and output channels.

See also: Read and write streams.

Solvers write on Python's sys.stdout by default, so output appears in the notebook:

In [1]:

from tuprolog.solve.prolog import prolog_solver

prolog_solver().solve_once("write('Hello from Prolog!'), nl").is_yes

from tuprolog.solve.prolog import prolog_solver prolog_solver().solve_once("write('Hello from Prolog!'), nl").is_yes

Hello from Prolog!

Out[1]:

True

Output can be captured in a Python stream instead, and input read from one (read/1 comes with IOLib, see below):

In [2]:

import io

from tuprolog.solve.libs import IOLib

output = io.StringIO()
solver = prolog_solver(libraries=IOLib, std_in=io.StringIO("likes(bart, skate). "), std_out=output)
solver.solve_once("read(T), write(got(T)), nl")
output.getvalue()

import io from tuprolog.solve.libs import IOLib output = io.StringIO() solver = prolog_solver(libraries=IOLib, std_in=io.StringIO("likes(bart, skate). "), std_out=output) solver.solve_once("read(T), write(got(T)), nl") output.getvalue()

Out[2]:

'got(likes(bart, skate))\n'

Theories can be read from files (or any text stream):

In [3]:

import os
import tempfile

from tuprolog.theory.parsing import read_theory

with tempfile.NamedTemporaryFile("w", suffix=".pl", delete=False) as file:
    file.write("color(red). color(green). color(blue).\n")
try:
    with open(file.name) as source:
        colors = read_theory(source)
finally:
    os.remove(file.name)
list(prolog_solver(static_kb=colors).query("color(C)"))

import os import tempfile from tuprolog.theory.parsing import read_theory with tempfile.NamedTemporaryFile("w", suffix=".pl", delete=False) as file: file.write("color(red). color(green). color(blue).\n") try: with open(file.name) as source: colors = read_theory(source) finally: os.remove(file.name) list(prolog_solver(static_kb=colors).query("color(C)"))

Out[3]:

[{'C': 'red'}, {'C': 'green'}, {'C': 'blue'}]

IOLib¶

IOLib (used above for read/1) adds ISO Prolog's stream predicates (open/3, read/2, write/2, close/1, ...), so Prolog code can manage files on its own, naming them by URIs for portability:

In [4]:

from pathlib import Path

path = Path(tempfile.mkdtemp(), "out.txt")
solver = prolog_solver(libraries=IOLib)
# IOLib opens files by URI (e.g. file:///tmp/out.txt), which works on every OS
solver.solve_once(f"open('{path.as_uri()}', write, S), write(S, hello(world)), nl(S), close(S)")
print(path.read_text())
path.unlink()

from pathlib import Path path = Path(tempfile.mkdtemp(), "out.txt") solver = prolog_solver(libraries=IOLib) # IOLib opens files by URI (e.g. file:///tmp/out.txt), which works on every OS solver.solve_once(f"open('{path.as_uri()}', write, S), write(S, hello(world)), nl(S), close(S)") print(path.read_text()) path.unlink()

hello(world)