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Arithmetic evaluation: Difference between revisions
→{{header|J}}: Better way to prevent eating of empties
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=={{header|J}}==
rules=: ''
patterns=: ,"0 assert 1
addrule=: dyad define
rules=: rules,;:x
patterns=: patterns,+./@classify"1 y
)
'Term' addrule '$()', '0', '+-',: '0'
'Factor' addrule '$()+-', '0', '*/',: '0'
'Parens' addrule '(', '*/+-0', ')',: ')*/+-0$'
rules=: rules,;:'Move'
buildTree=: monad define
words=: ;:'$',y
queue=: classify '$',y
stack=: classify '$$$$'
tokens=: ]&.>i.#words
tree=: ''
while.(#queue)+.6<#stack do.
rule=: rules {~ i.&1 patterns (*./"1)@:(+./"1) .(*."1)4{.stack
rule`:6''
end.
'syntax' assert 1 0 1 1 1 1 -: {:"1 stack
gerund=: literal&.> (<,'%') (I. words=<,'/')} words
gerund;1{tree
)
literal=:monad define ::]
".'t=.',y
5!:1<'t'
)
Term=: Factor=: monad define
stack=: ({.stack),(classify '0'),4}.stack
tree=: ({.tree),(<1 2 3{tree),4}.tree
)
stack=: (1{stack),3}.stack
tree=: (1{tree),3}.tree
'syntax' assert 0<#queue
queue=: }:queue
tree=: ({:tokens),tree
tokens=: }:tokens
)
parse=:monad define
tmp=: conew 'parser'
r=: buildTree__tmp y
coerase tmp
r
)</lang>
example use:
eval parse '1+2*3/(4-5+6)'
2.2
You can also display the syntax tree, for example:
=={{header|Pascal}}==
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