Consider my simple grammar, skipping the lexer here:

expr:
    expr expr+                           # CallFormExpr // ⬅ the question here!
    | L_PAREN expr R_PAREN               # ParensExpr
    | L_BRACKET (expr COMMA?)* R_BRACKET # SquareBracketExpr
    | L_CURLY (expr COMMA?)* R_CURLY     # CurlyBracesExpr
    | lit                                # LitExpr
    | ident                              # IdentExpr
;

ident : IDENTIFIER | OPERATOR;

lit:
    RUNE_LIT
    | RAW_STRING_LIT
    | INTERPRETED_STRING_LIT
    | IMAGINARY_LIT
    | FLOAT_LIT
    | DECIMAL_LIT
    | BINARY_LIT
    | OCTAL_LIT
    | HEX_LIT
;

Now, the very first expr option expr expr+ is meant to capture foo bar baz as an expr with 3 idents but Antlr4 Lab gives me this parse tree which is kind of akin to foo (bar baz):

Due to recursion, the “flat list gets treeified”. Is it a matter of how the expr options are ordered? Or is there some Antlr “hinting syntax” to “keep it flat”?