From 67da4d2df143f6c9945b8f1da0a7297d26aee566 Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Sun, 26 Aug 2012 02:25:41 -0400
Subject: [PATCH] Add parsing and representation of slices.
---
pymbolic/parser.py | 41 ++++++++++++++++++++++++++++++++++++++-
pymbolic/primitives.py | 44 ++++++++++++++++++++++++++++++++++++++++++
test/test_pymbolic.py | 12 ++++++++++++
3 files changed, 96 insertions(+), 1 deletion(-)
diff --git a/pymbolic/parser.py b/pymbolic/parser.py
index 864cfd9..c49e636 100644
--- a/pymbolic/parser.py
+++ b/pymbolic/parser.py
@@ -16,6 +16,7 @@ _identifier = intern("identifier")
_whitespace = intern("whitespace")
_comma = intern("comma")
_dot = intern("dot")
+_colon = intern("colon")
_equal = intern("equal")
_notequal = intern("notequal")
@@ -29,6 +30,7 @@ _or = intern("or")
_not = intern("not")
_PREC_COMMA = 5 # must be > 1 (1 is used by fortran-to-cl)
+_PREC_SLICE = 10
_PREC_LOGICAL_OR = 80
_PREC_LOGICAL_AND = 90
_PREC_COMPARISON = 100
@@ -41,6 +43,13 @@ _PREC_CALL = 150
+def _join_to_slice(left, right):
+ from pymbolic.primitives import Slice
+ if isinstance(right, Slice):
+ return Slice((left,) + right.children)
+ else:
+ return Slice((left, right))
+
class Parser:
lex_table = [
(_equal, pytools.lex.RE(r"==")),
@@ -76,6 +85,7 @@ class Parser:
(_whitespace, pytools.lex.RE("[ \n\t]*")),
(_comma, pytools.lex.RE(",")),
(_dot, pytools.lex.RE(r"\.")),
+ (_colon, pytools.lex.RE(r"\:")),
]
_COMP_TABLE = {
@@ -107,7 +117,20 @@ class Parser:
import pymbolic.primitives as primitives
pstate.expect_not_end()
- if pstate.is_next(_times):
+ if pstate.is_next(_colon):
+ pstate.advance()
+
+ expr_pstate = pstate.copy()
+ from pytools.lex import ParseError
+ try:
+ next_expr = self.parse_expression(expr_pstate, _PREC_SLICE)
+ except ParseError:
+ # no expression follows, too bad.
+ left_exp = primitives.Slice((None,))
+ else:
+ left_exp = _join_to_slice(None, next_expr)
+ pstate.assign(expr_pstate)
+ elif pstate.is_next(_times):
pstate.advance()
left_exp = primitives.Wildcard()
elif pstate.is_next(_plus):
@@ -222,6 +245,22 @@ class Parser:
self._COMP_TABLE[next_tag],
self.parse_expression(pstate, _PREC_COMPARISON))
did_something = True
+ elif next_tag is _colon and _PREC_SLICE >= min_precedence:
+ pstate.advance()
+ expr_pstate = pstate.copy()
+
+ assert not isinstance(left_exp, primitives.Slice)
+
+ from pytools.lex import ParseError
+ try:
+ next_expr = self.parse_expression(expr_pstate, _PREC_SLICE)
+ except ParseError:
+ # no expression follows, too bad.
+ left_exp = primitives.Slice((left_exp, None,))
+ else:
+ left_exp = _join_to_slice(left_exp, next_expr)
+ pstate.assign(expr_pstate)
+
elif next_tag is _comma and _PREC_COMMA > min_precedence:
# The precedence makes the comma left-associative.
diff --git a/pymbolic/primitives.py b/pymbolic/primitives.py
index 91e63a5..2d67adb 100644
--- a/pymbolic/primitives.py
+++ b/pymbolic/primitives.py
@@ -727,6 +727,50 @@ class Derivative(Expression):
mapper_method = intern("map_derivative")
+
+
+
+class Slice(Expression):
+ """A slice expression as in a[1:7]."""
+
+ def __init__(self, children):
+ assert isinstance(children, tuple)
+ self.children = children
+
+ if len(children) > 3:
+ raise ValueError("slice with more than three arguments")
+
+ def __getinitargs__(self):
+ return (self.children,)
+
+ def __nonzero__(self):
+ return True
+
+ @property
+ def start(self):
+ if len(self.children) > 1:
+ return self.children[0]
+ else:
+ return None
+
+ @property
+ def stop(self):
+ if len(self.children) == 1:
+ return self.children[0]
+ elif len(self.children) > 1:
+ return self.children[1]
+ else:
+ return None
+
+ @property
+ def step(self):
+ if len(self.children) == 3:
+ return self.children[2]
+ else:
+ return None
+
+ mapper_method = intern("map_slice")
+
# }}}
# intelligent factory functions ----------------------------------------------
diff --git a/test/test_pymbolic.py b/test/test_pymbolic.py
index 396fda0..09f74cc 100644
--- a/test/test_pymbolic.py
+++ b/test/test_pymbolic.py
@@ -142,6 +142,18 @@ def test_parser():
print repr(parse("a >= 1"))
print repr(parse("a <= 1"))
+ print repr(parse(":"))
+ print repr(parse("1:"))
+ print repr(parse(":2"))
+ print repr(parse("1:2"))
+ print repr(parse("::"))
+ print repr(parse("1::"))
+ print repr(parse(":1:"))
+ print repr(parse("::1"))
+ print repr(parse("3::1"))
+ print repr(parse(":5:1"))
+ print repr(parse("3:5:1"))
+
--
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