Use left recursive grammar in peg.expr

db4
Chris Double 2008-03-30 17:23:11 +13:00
parent af9e27823a
commit d002e02948
1 changed files with 10 additions and 15 deletions
extra/peg/expr

View File

@ -4,24 +4,19 @@ USING: kernel arrays strings math.parser sequences
peg peg.ebnf peg.parsers memoize math ;
IN: peg.expr
: operator-fold ( lhs seq -- value )
#! Perform a fold of a lhs, followed by a sequence of pairs being
#! { operator rhs } in to a tree structure of the correct precedence.
swap [ first2 swap call ] reduce ;
EBNF: expr
times = "*" [[ drop [ * ] ]]
divide = "/" [[ drop [ / ] ]]
add = "+" [[ drop [ + ] ]]
subtract = "-" [[ drop [ - ] ]]
digit = [0-9] => [[ digit> ]]
number = (digit)+ => [[ 10 digits>integer ]]
value = number
| ("(" exp ")") => [[ second ]]
digit = [0-9] [[ digit> ]]
number = (digit)+ [[ unclip [ swap 10 * + ] reduce ]]
fac = fac "*" value => [[ first3 nip * ]]
| fac "/" value => [[ first3 nip / ]]
| number
value = number | ("(" expr ")") [[ second ]]
product = (value ((times | divide) value)*) [[ first2 operator-fold ]]
sum = (product ((add | subtract) product)*) [[ first2 operator-fold ]]
expr = sum
exp = exp "+" fac => [[ first3 nip + ]]
| exp "-" fac => [[ first3 nip - ]]
| fac
;EBNF
: eval-expr ( string -- number )