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(ns cljcc.parser
(:require
[cljcc.lexer :as l]
[cljcc.token :as t]
[clojure.pprint :as pp]))
(declare parse parse-exp)
(defn- keyword->type [k]
(condp = k
:kw-int "int"
(throw (ex-info "Parser Error. Unsupported type." {:keyword k}))))
(defn- expect
"Expects the first token in list to be of given kind.
Returns the token and remaining tokens."
[kind [token & rst]]
(if (= kind (:kind token))
[token rst]
(throw (ex-info "Parser Error." {:expected kind
:actual (:kind token)}))))
(defn- expect-in [kinds [{kind :kind :as token} & rst]]
(if (contains? kinds kind)
[token rst]
(throw (ex-info "Parser Error." {:expected kinds
:actual token}))))
(defn constant-exp-node [v]
{:type :exp
:exp-type :constant-exp
:value v})
(defn variable-exp-node [identifier]
{:type :exp
:exp-type :variable-exp
:identifier identifier})
(defn unary-exp-node [op v]
{:type :exp
:exp-type :unary-exp
:unary-operator op
:value v})
(defn binary-exp-node [l r op]
{:type :exp
:exp-type :binary-exp
:binary-operator op
:left l
:right r})
(defn assignment-exp-node [l r op]
{:type :exp
:exp-type :assignment-exp
:assignment-operator op
:left l
:right r})
(defn- parse-factor [[{kind :kind :as token} :as tokens]]
(cond
(= kind :number) [(constant-exp-node (:literal token)) (rest tokens)]
(t/unary-op? kind) (let [op kind
[e rst] (parse-factor (rest tokens))]
[(unary-exp-node op e) rst])
(= kind :left-paren) (let [[e rst] (parse-exp (rest tokens))
[_ rst] (expect :right-paren rst)]
[e rst])
(= kind :identifier) [(variable-exp-node (:literal token)) (rest tokens)]
:else (throw (ex-info "Parser Error. Malformed token." {:token token}))))
(defn- parse-exp
([tokens]
(parse-exp tokens 0))
([tokens min-prec]
(loop [[left rst] (parse-factor tokens)
tokens rst]
(let [[{kind :kind :as _token} :as tokens] tokens]
(if (and (t/binary-op? kind) (>= (t/precedence kind) min-prec))
(if (t/assignment-op? kind)
(let [[_ tokens] (expect kind tokens)
[right rst] (parse-exp tokens (t/precedence kind))]
(recur [(assignment-exp-node left right kind)] rst))
(let [[right rst] (parse-exp (rest tokens) (+ (t/precedence kind) 1))]
(recur [(binary-exp-node left right kind)] rst)))
[left tokens])))))
(defn return-statement-node [e]
{:type :statement
:statement-type :return
:value e})
(defn expression-statement-node [e]
{:type :statement
:statement-type :expression
:value e})
(defn empty-statement-node []
{:type :statement
:statement-type :empty})
(defn- parse-return-statement [tokens]
(let [[_ rst] (expect :kw-return tokens)
[exp-node rst] (parse-exp rst)
[_ rst] (expect :semicolon rst)]
[(return-statement-node exp-node) rst]))
(defn- parse-expression-statement [tokens]
(let [[exp-node rst] (parse-exp tokens)
[_ rst] (expect :semicolon rst)]
[(expression-statement-node exp-node) rst]))
(defn- parse-empty-statement
"Parses statement expect only single semicolon"
[tokens]
(let [[_ rst] (expect :semicolon tokens)]
[(empty-statement-node) rst]))
(defn- parse-statement
"Parses a single statement. Expects a semicolon at the end."
[[{kind :kind} :as tokens]]
(cond
(= kind :semicolon) (parse-empty-statement tokens)
(= kind :kw-return) (parse-return-statement tokens)
:else (parse-expression-statement tokens)))
(defn declaration-node
([identifier] {:type :declaration
:identifier identifier})
([identifier v] {:type :declaration
:identifier identifier
:initial v}))
(defn- parse-declaration [tokens]
(let [[_ rst] (expect :kw-int tokens)
[ident-token rst] (expect :identifier rst)
[{kind :kind} :as tokens] rst]
(cond
(= kind :semicolon) (let [[_ rst] (expect :semicolon tokens)]
[(declaration-node (:literal ident-token)) rst])
(= kind :assignment) (let [[_ rst] (expect :assignment tokens)
[exp-node rst] (parse-exp rst)
[_ rst] (expect :semicolon rst)]
[(declaration-node (:literal ident-token) exp-node) rst])
:else (throw (ex-info "Parser error. Declaration error parsing." {})))))
(defn- parse-block-item [[token :as tokens]]
(if (= :kw-int (:kind token))
(parse-declaration tokens)
(parse-statement tokens)))
(defn- parse-repeatedly [tokens parse-f end-kind]
(loop [tokens tokens
res []]
(if (= end-kind (:kind (first tokens)))
[res tokens]
(let [[node rst] (parse-f tokens)]
(recur rst (conj res node))))))
(defn- parse-function [tokens]
(let [[fn-type-token rst] (expect :kw-int tokens)
[fn-identifier-token rst] (expect :identifier rst)
[_ rst] (expect :left-paren rst)
[fn-parameter-token rst] (expect :kw-void rst)
[_ rst] (expect :right-paren rst)
[_ rst] (expect :left-curly rst)
[block-items rst] (parse-repeatedly rst parse-block-item :right-curly)
[_ rst] (expect :right-curly rst)]
[{:type :function
:return-type (keyword->type (:kind fn-type-token))
:identifier (:literal fn-identifier-token)
:parameters (:kind fn-parameter-token)
:body block-items}
rst]))
(defn- parse-program [tokens]
(let [[ast rst] (parse-function tokens)
_ (expect :eof rst)]
[ast]))
(defn parse [tokens]
(-> tokens
:tokens
parse-program))
(defn parse-from-src [src]
(-> src
l/lex
parse))
(comment
(pp/pprint (parse-from-src "
int main(void) {
int a = b = 4;
int var0 = 2;
var0 = 41;
}"))
(pp/pprint
(l/lex
"int main(void) {return 1 + 2;}"))
(pp/pprint
(l/lex "
int main(void) {
return 2;
}"))
(parse "int main(void) {
return -(((((10)))));
}")
(pp/pprint (parse "int main(void) {
return 1 & 2 + 6 & 6;
}"))
())
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