Recursive descent parser generator: Difference between revisions

=={{header|J}}==

J's recursive descent parser is adequate for this task, if we map names appropriately.

Implementation:

<lang J>cocurrent 'base'

inlocale=: 4 :0 L:0

x,'_',y,'_'

)

parse=: 3 :0

sentence=. ;:y

opinds=. (;:'+*-')i.sentence

opfuns=. (;:'plus times minus') inlocale 'base'

scratch=. cocreate''

coinsert__scratch 'base'

names=. ~.sentence#~_1<:nc sentence

(names inlocale scratch)=: names

do__scratch ;:inv opinds}((#sentence)#"0 opfuns),sentence

)

op=: 1 :0

:

r=. genname''

emit r,'=:',x,m,y

r

)

plus=: '+' op

times=: '*' op

minus=: '-' op

N=: 10000

genname=: 3 :0

'z',}.":N=: N+1

)

emit=: smoutput</lang>

Task example:

<lang J> parse'(one + two) * three - four * five'

z0001=:four*five

z0002=:three-z0001

z0003=:one+two

z0004=:z0003*z0002

z0004</lang>