I am trying to implement a grammar for a simple if..then..else statement along with simple statements.
It should be able to parse a statement like:
if things are going fine
then
things are supposed to be this way
just go with it
else
nothing new
How are you?
The document starts with a decision (if.. then.. else) and is followed by a simple statement.
My grammar so far looks like this:
document = decision / simple_statement / !.
decision = i:if t:then e:(else)? document { return { if: { cond: i }, then: t, else: e } }
if = 'if' s:statement nl { return s }
then = 'then' nl actions:indented_statements+ { return actions }
else = 'else' nl actions:indented_statements+ { return actions }
indented_statements = ss:(tab statement nl)+ { return ss.reduce(function(st, el) { return st.concat(el) }, []) }
statement = text:$(char+) { return text.trim() }
simple_statement = s:statement nl document { return { action: s } }
char = [^\n\r]
ws = [ \t]*
tab = [\t]+ { return '' }
nl = [\r\n]+
This returns an output:
{
"if": {
"cond": "things are going fine"
},
"then": [
[
"",
"things are supposed to be this way",
[
"
"
],
"",
"just go with it",
[
"
"
]
]
],
"else": [
[
"",
"nothing new",
[
"
"
]
]
]
}
1. Why are there extra empty strings and arrays in the then
and else
array? What should I do to remove them?
EDIT: I think I figured out why I was getting the arrays. I changed the grammar to remove repetitions inside indented_statements
.
document = decision / simple_statement / !.
decision = i:if t:then e:(else)? document { return { if: i, then: t, else: e } }
if = 'if' s:statement nl { return s }
then = 'then' nl actions:indented_statements+ { return actions }
else = 'else' nl actions:indented_statements+ { return actions }
indented_statements = tab s:statement nl { return s }
statement = text:$(char+) { return text.trim() }
simple_statement = s:statement nl document { return { action: s } }
char = [^\n\r]
ws = [ \t]*
tab = [\t]+ { return '' }
nl = [\r\n]+
I figured out the answer. I needed to provide the first statement as repeating:
document = (decision / simple_statement)*