S-expressions
editable example
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ghul
use IO.Std.write_line
use Ghul.Pipes
union SExpr is
LIST(items: SExpr[])
SYMBOL(name: string)
STRING(text: string)
INTEGER(value: int)
REAL(value: double)
si
use SExpr.LIST
use SExpr.SYMBOL
use SExpr.STRING
use SExpr.INTEGER
use SExpr.REAL
delimits(character: char) -> bool =>
character == '(' \/ character == ')' \/
character == '"' \/ character <= ' '
skip_space(text: string, at: int) -> int is
let i mut = at
while i < text.length /\ text[i] <= ' ' do
i = i + 1
od
return i
si
atom(token: string) -> SExpr is
let whole mut = 0
if int.try_parse(token, whole ref) then
return INTEGER(whole)
fi
let real mut = 0.0D
if double.try_parse(token, real ref) then
return REAL(real)
fi
return SYMBOL(token)
si
read(text: string, at: int) -> (value: SExpr, next: int) is
let start = skip_space(text, at)
if text[start] == '(' then
let items = Collections.LIST[SExpr]()
let i mut = skip_space(text, start + 1)
while text[i] != ')' do
let (value, next) = read(text, i)
items.add(value)
i = skip_space(text, next)
od
return (value = LIST(items.to_array()), next = i + 1)
fi
if text[start] == '"' then
let close mut = start + 1
while text[close] != '"' do
close = close + 1
od
return (value = STRING(text[start + 1..close]), next = close + 1)
fi
let end mut = start
while end < text.length /\ !delimits(text[end]) do
end = end + 1
od
return (value = atom(text[start..end]), next = end)
si
render(node: SExpr) -> string =>
case ►node
when (items): LIST then "({items |> map(render) |> join(" ")})"
when (name): SYMBOL then name
when (text): STRING then "\"{text}\""
when (value): INTEGER then "{value}"
when (value): REAL then "{value}"
esac
let source =
"((data \"quoted data\" 123 4.5)\n"
" (data (!@# (4.5) \"(more\" \"data)\")))"
let (parsed, _) = read(source, 0)
write_line(source)
write_line("")
write_line(render(parsed))