From 4d9b2ea05089a7ae6908a624d56c3f1ac5193d4b Mon Sep 17 00:00:00 2001
From: Dominic Kempf <dominic.kempf@iwr.uni-heidelberg.de>
Date: Thu, 7 Sep 2017 20:55:02 +0200
Subject: [PATCH] Have maxima parser recognize exponential functions

Maxima represents exp(x) as "%e^x". This enhances the
parser to recognize the special symbol %e and have any
power function with it as a base return exp instead of
pow.
---
 pymbolic/interop/maxima.py | 14 ++++++++++++--
 test/test_maxima.py        |  1 +
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/pymbolic/interop/maxima.py b/pymbolic/interop/maxima.py
index 2dabf2b..e2c624c 100644
--- a/pymbolic/interop/maxima.py
+++ b/pymbolic/interop/maxima.py
@@ -40,6 +40,7 @@ import six
 from six.moves import intern
 import re
 import pytools
+import numpy as np
 
 from pymbolic.mapper.stringifier import StringifyMapper
 from pymbolic.parser import Parser as ParserBase, FinalizedTuple
@@ -92,10 +93,12 @@ class MaximaStringifyMapper(StringifyMapper):
 class MaximaParser(ParserBase):
     power_sym = intern("power")
     imag_unit = intern("imag_unit")
+    euler_number = intern("euler_number")
 
     lex_table = [
             (power_sym, pytools.lex.RE(r"\^")),
             (imag_unit, pytools.lex.RE(r"%i")),
+            (euler_number, pytools.lex.RE(r"%e")),
             ] + ParserBase.lex_table
 
     def parse_prefix(self, pstate):
@@ -126,6 +129,9 @@ class MaximaParser(ParserBase):
         elif next_tag is self.imag_unit:
             pstate.advance()
             return 1j
+        elif next_tag is self.euler_number:
+            pstate.advance()
+            return np.e
         elif next_tag is p._identifier:
             if six.PY3:
                 return primitives.Variable(pstate.next_str_and_advance())
@@ -158,7 +164,6 @@ class MaximaParser(ParserBase):
                 pstate.advance()
 
                 if left_exp == primitives.Variable("matrix"):
-                    import numpy as np
                     left_exp = np.array(list(list(row) for row in args))
                 else:
                     left_exp = primitives.Call(left_exp, args)
@@ -197,7 +202,12 @@ class MaximaParser(ParserBase):
             did_something = True
         elif next_tag is self.power_sym and p._PREC_POWER > min_precedence:
             pstate.advance()
-            left_exp **= self.parse_expression(pstate, p._PREC_POWER)
+            exponent = self.parse_expression(pstate, p._PREC_POWER)
+            if left_exp == np.e:
+                from pymbolic.primitives import Call, Variable
+                left_exp = Call(Variable("exp"), (exponent,))
+            else:
+                left_exp **= exponent
             did_something = True
         elif next_tag is p._comma and p._PREC_COMMA > min_precedence:
             # The precedence makes the comma left-associative.
diff --git a/test/test_maxima.py b/test/test_maxima.py
index 7ddbb68..7bd2ad6 100644
--- a/test/test_maxima.py
+++ b/test/test_maxima.py
@@ -74,6 +74,7 @@ def test_strict_round_trip(knl):
             2j,
             parse("x**y"),
             Quotient(1, 2),
+            parse("exp(x)")
             ]
     for expr in exprs:
         result = knl.eval_expr(expr)
-- 
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