Lilac parser
A toy DSL-based combinator parser with better failure reasons.
Online demo http://repo.mvc-works.org/lilac-parser/
Try with (def a (add 1 2)) or {"json": [1, 2]}.
Usage
[mvc-works/lilac-parser "0.0.3-a3"]
(require '[lilac-parser.core :refer
[parse-lilac defparser is+ many+ one-of+ other-than+
some+ combine+ interleave+ label+
replace-lilac]])
(parse-lilac (string/split "aaaa" "") (many+ (is+ "a")))
Demo of a stupid S-expression parser:
(def number-parser (many+ (one-of+ "1234567890")))
(def space-parser (is+ " "))
(def word-parser (many+ (one-of+ "qwertyuiopasdfghjklzxcvbnm")))
(defparser
s-expr-parser+
()
identity
(combine+
[(is+ "(")
(some+ (or+ [number-parser word-parser space-parser (s-expr-parser+)]))
(is+ ")")]))
(parse-lilac (string/split "(def a (add 1 2))" "") (s-expr-parser+))
Rules
| Rule | Example | Description |
|---|---|---|
is+ | (is+ "a") or (is+ "abc") | matches a piece of string |
one-of+ | (one-of+ "abc") or (one-of+ #{"a" "b" "c"}) | matches a character in one of candidates |
other-than+ | (other-than+ "abc") | matches a character that is not listed |
optional+ | (optional+ (is+ "a")) | matching or nothing |
some+ | (some+ (is+ "a")) | matches 0 or more items |
many+ | (many+ (is+ "a")) | matches 1 or more items |
or+ | (or+ [(is+ "a") (is+ "b")]) | matches one among listed items |
combine+ | (combine+ [(is+ "a") (is+ "b")]) | matches items in ecxact order |
interleave+ | (interleave+ (is+ "a") (is+ ",")) | matches two interleaving items |
label+ | (label+ "just a" (is+ "a")) | simpler rule for adding comments in result |
defparser
defparser is a macro for defining parser that can be used recursively. The type is :component, which is like a more complicated version of :label. Notice that s-expr-parser+ defined with defparser is different from a normal rule, it's a function so it need to be called before being used as a rule.
Visual DEMO
lilac-parser would be pretter slow since it tries to store all information during parsing, which results in a piece of EDN data. The result can be rendered into a tree with GUI and that's what is demonstrated in the demo.
An example for EDN data in parsing a JSON number.
{
:ok? true, :value 112, :parser-node :component, :label :value-parser+
:rest ("," "1")
:result {
:ok? true, :value 112, :parser-node :or
:rest ("," "1")
:result {
:ok? true, :parser-node :label, :label "number", :value 112
:rest ("," "1")
:result {
:ok? true, :value 112, :parser-node :combine
:rest ("," "1")
:results [
{
:ok? true, :value nil, :parser-node :optional
:result {
:ok? false, :message "expects \"-\" but got \"1\"", :parser-node :is
:rest ["1" "1" "2" "," "1"]
}
:rest ["1" "1" "2" "," "1"]
}
{
:ok? true, :parser-node :many
:value ("1" "1" "2")
:rest ("," "1")
:results [
{
:ok? true, :value "1", :parser-node :one-of
:rest ("1" "2" "," "1")
}
{
:ok? true, :value "1", :parser-node :one-of
:rest ("2" "," "1")
}
{
:ok? true, :value "2", :parser-node :one-of
:rest ("," "1")
}
]
:peek-result {
:ok? false, :message "\",\" is not in \"1234567890\"", :parser-node :one-of
:rest ("," "1")
}
}
{
:ok? true, :value nil, :parser-node :optional
:result {
:ok? false, :parser-node :combine, :message "failed to combine"
:result {
:ok? false, :message "expects \".\" but got \",\"", :parser-node :is
:rest ("," "1")
}
:previous-results []
:rest ("," "1")
}
:rest ("," "1")
}
]
}
}
}
}
Custom Rule
Parser rules can be expected by injecting functions. It could be quite tricky and is not recommended:
(lilac-parser.core/resigter-custom-rule! :xyz
(fn [xs rule]
; TODO
))
(defn xyz+ [xs transform]
; TODO
)
Replacer
A function is also provided for replacing text pieces matching a given rule:
(replace-lilac (string/split content "") rule (fn [x] (str "<<<" x ">>>>")))
which returns :result as well as parsing details in :attempts:
{
:result "<<<MATCHED>>>>"
:attempts [
; parsing summaries in vector
]
}
This is an experimental API serving jobs as a custom regular expression replacer.
Workflow
Workflow https://github.com/mvc-works/calcit-workflow
License
MIT
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