From e72ebf59e270a43bd20c5693d7056d0e89078f0e Mon Sep 17 00:00:00 2001
From: Valentin Gehrke <madmaurice@zom.bi>
Date: Sun, 20 Nov 2016 10:55:44 +0100
Subject: [PATCH] First LL parser
---
ll.py | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 79 insertions(+)
create mode 100644 ll.py
diff --git a/ll.py b/ll.py
new file mode 100644
index 0000000..99eca51
--- /dev/null
+++ b/ll.py
@@ -0,0 +1,79 @@
+#!/usr/bin/env python
+
+TS_A = 'a'
+TS_B = 'b'
+TS_PLUS = '+'
+TS_MULT = '*'
+SYM_END = object()
+NTS_E = 1
+NTS_T = 2
+NTS_F = 3
+
+# 1. E -> E + T
+# 2. E -> T
+# 3. T -> T * F
+# 4. T -> F
+# 5. F -> 'a'
+
+# 1. E -> T F
+# 2. F -> '+' T F
+# 3. F ->
+# 4. T -> 'b'
+# 5. T -> 'a'
+
+table = {
+ NTS_E : {
+ TS_A: 1,
+ TS_B: 1,
+ },
+ NTS_F : {
+ TS_PLUS: 2,
+ SYM_END: 3
+ },
+ NTS_T : {
+ TS_A: 4,
+ TS_B: 5
+ }
+}
+
+def tparse(text):
+ stack = []
+ stack.append(NTS_E);
+ while len(stack) > 0:
+ if len(text) == 0:
+ c = SYM_END
+ else:
+ c = text[0]
+ if c == stack[-1]:
+ text = text[1:]
+ stack.pop()
+ else:
+ try:
+ rule = table[stack[-1]][c]
+ except KeyError:
+ print("Unexpected %s" % c)
+ return
+ if rule == 1:
+ stack.pop()
+ stack.append(NTS_F)
+ stack.append(NTS_T)
+ elif rule == 2:
+ stack.pop()
+ stack.append(NTS_F)
+ stack.append(NTS_T)
+ stack.append(TS_PLUS)
+ elif rule == 3:
+ stack.pop()
+ elif rule == 4:
+ stack.pop()
+ stack.append(TS_A)
+ elif rule == 5:
+ stack.pop()
+ stack.append(TS_B)
+ else:
+ print("Unexpected %s" % (text[0]))
+ return
+ print("Applied rule %d" % rule)
+
+if __name__ == '__main__':
+ tparse("b+a+b+b+a")