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| author | sienkiew <sienkiew@d34015c8-bcbb-4646-8ac8-8ba5febf221d> | 2011-07-21 11:17:58 -0400 |
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| committer | sienkiew <sienkiew@d34015c8-bcbb-4646-8ac8-8ba5febf221d> | 2011-07-21 11:17:58 -0400 |
| commit | be5a70d3aa1c30d7c86d77649b747de2838566ce (patch) | |
| tree | 7c27103a4d37b61f5dba748672f0685536e667d0 /examples/expr.g | |
| parent | 77ce1e78848ba9eead2566e3bc55523aab4547e8 (diff) | |
| download | exyapps-be5a70d3aa1c30d7c86d77649b747de2838566ce.tar.gz | |
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
Diffstat (limited to 'examples/expr.g')
| -rw-r--r-- | examples/expr.g | 21 |
1 files changed, 21 insertions, 0 deletions
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 }} |