From be5a70d3aa1c30d7c86d77649b747de2838566ce Mon Sep 17 00:00:00 2001
From: sienkiew <sienkiew@d34015c8-bcbb-4646-8ac8-8ba5febf221d>
Date: Thu, 21 Jul 2011 15:17:58 +0000
Subject: initial import of yapps from debian sources

git-svn-id: http://svn.stsci.edu/svn/ssb/etal/exyapps/trunk@356 d34015c8-bcbb-4646-8ac8-8ba5febf221d
---
 examples/expr.g | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100644 examples/expr.g

(limited to 'examples/expr.g')

diff --git a/examples/expr.g b/examples/expr.g
new file mode 100644
index 0000000..ae807b7
--- /dev/null
+++ b/examples/expr.g
@@ -0,0 +1,21 @@
+parser Calculator:
+    token END: "$"
+    token NUM: "[0-9]+"
+
+    rule goal:           expr END         {{ return expr }}
+
+    # An expression is the sum and difference of factors
+    rule expr:           factor           {{ v = factor }}
+                       ( "[+]" factor       {{ v = v+factor }}
+                       |  "-"  factor       {{ v = v-factor }}
+                       )*                 {{ return v }}
+
+    # A factor is the product and division of terms
+    rule factor:         term             {{ v = term }}
+                       ( "[*]" term         {{ v = v*term }}
+                       |  "/"  term         {{ v = v/term }}
+                       )*                 {{ return v }}
+
+    # A term is either a number or an expression surrounded by parentheses
+    rule term:           NUM              {{ return atoi(NUM) }}
+                       | "\\(" expr "\\)" {{ return expr }}
-- 
cgit