Rename enable_left_recursion to enableLeftRecursion for consistency with other pyparsing names (left in enable_left_recursion synonym as omen of names to come); added notes to CHANGES and whats_new_in_3_0_0.rst; added left_recursion.py to examples.

1 files changed, 45 insertions, 0 deletions

diff --git a/examples/left_recursion.py b/examples/left_recursion.py
new file mode 100644
index 0000000..f3977dc
--- /dev/null
+++ b/examples/left_recursion.py
@@ -0,0 +1,45 @@
+#
+# left_recursion.py
+#
+# Example code illustrating use of left-recursion in Pyparsing.
+#
+import pyparsing as pp
+
+# comment out this line to see the effects without LR parsing enabled
+pp.ParserElement.enableLeftRecursion()
+
+item_list = pp.Forward()
+
+# a common left-recursion definition
+# define a list of items as 'list + item | item'
+# BNF:
+#   item_list := item_list item | item
+#   item := word of alphas
+item = pp.Word(pp.alphas)
+item_list <<= item_list + item | item
+
+item_list.runTests("""\
+    To parse or not to parse that is the question
+    """)
+
+# Define a parser for an expression that can be an identifier, a quoted string, or a
+# function call that starts with an expression
+# BNF:
+#   expr := function_call | name | string | '(' expr ')'
+#   function_call := expr '(' expr,... ')'
+#   name := Python identifier
+#   string := a quoted string
+# from https://stackoverflow.com/questions/32809389/parse-python-code-using-pyparsing/32822575#32822575
+
+LPAR, RPAR = map(pp.Suppress, "()")
+expr = pp.Forward()
+string = pp.quotedString
+function_call = expr + pp.Group(LPAR + pp.Optional(pp.delimitedList(expr)) + RPAR)
+name = pp.Word(pp.alphas + '_', pp.alphanums + '_')
+# left recursion - call starts with an expr
+expr <<= function_call | string | name | pp.Group(LPAR + expr + RPAR)
+
+expr.runTests("""\
+    print("Hello, World!")
+    (lookup_function("fprintf"))(stderr, "Hello, World!")
+    """, fullDump=False)