Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!
If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.
sig type token = AMPERAMPER | AMPERSAND | AND | AS | ASSERT | BACKQUOTE | BANG | BAR | BARBAR | BARRBRACKET | BEGIN | CHAR of char | CLASS | COLON | COLONCOLON | COLONEQUAL | COLONGREATER | COMMA | CONSTRAINT | DO | DONE | DOT | DOTDOT | DOWNTO | ELSE | END | EOF | EQUAL | EXCEPTION | EXTERNAL | FALSE | FLOAT of string | FOR | FUN | FUNCTION | FUNCTOR | GREATER | GREATERRBRACE | GREATERRBRACKET | IF | IN | INCLUDE | INFIXOP0 of string | INFIXOP1 of string | INFIXOP2 of string | INFIXOP3 of string | INFIXOP4 of string | INHERIT | INITIALIZER | INT of int | INT32 of int32 | INT64 of int64 | LABEL of string | LAZY | LBRACE | LBRACELESS | LBRACKET | LBRACKETBAR | LBRACKETLESS | LBRACKETGREATER | LBRACKETPERCENT | LBRACKETPERCENTPERCENT | LESS | LESSMINUS | LET | LIDENT of string | LPAREN | LBRACKETAT | LBRACKETATAT | LBRACKETATATAT | MATCH | METHOD | MINUS | MINUSDOT | MINUSGREATER | MODULE | MUTABLE | NATIVEINT of nativeint | NEW | NONREC | OBJECT | OF | OPEN | OPTLABEL of string | OR | PERCENT | PLUS | PLUSDOT | PLUSEQ | PREFIXOP of string | PRIVATE | QUESTION | QUOTE | RBRACE | RBRACKET | REC | RPAREN | SEMI | SEMISEMI | SHARP | SHARPOP of string | SIG | STAR | STRING of (string * string option) | STRUCT | THEN | TILDE | TO | TRUE | TRY | TYPE | UIDENT of string | UNDERSCORE | VAL | VIRTUAL | WHEN | WHILE | WITH | COMMENT of (string * Location.t) | DOCSTRING of Docstrings.docstring | EOL val implementation : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.structure val interface : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.signature val toplevel_phrase : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.toplevel_phrase val use_file : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.toplevel_phrase list val parse_core_type : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.core_type val parse_expression : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.expression val parse_pattern : (Lexing.lexbuf -> Parser.token) -> Lexing.lexbuf -> Parsetree.pattern end