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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 41 |
1 files changed, 41 insertions, 0 deletions
@@ -9181,6 +9181,47 @@ or an atom as .codn "(. sym)" . +.NP* Referencing Dot + +A dot token which is flanked by expressions on both sides, without any +intervening whitespace, is the referencing dot, and not the consing dot. +The referencing dot is a syntactic sugar which translated to the +.code qref +syntax ("quoted ref"), which currently has no assigned meaning and is reserved +for a future language extension. The referencing dot obeys these +correspondences: + +.cblk + ;; a.b may be almost any expressions + a.b <--> (qref a b) + a.b.c <--> (qref a b c) + a.(qref b c) <--> (qref a b c) + (qref a b).c <--> (qref (qref a b) c) +.cble + +That is to say, this dot operator constructs a +.code qref +expression out of its left and right arguments. If the right argument +of the dot is already a qref expression (whether produced by another instance +of the dot operator, or expressed directly) it is merged. And the qref dot +operator is right-to-left associative, so that +.code a.b.c +first produces +.code (qref b c) +via the right dot, and then +.code a +is adjoined into the syntax via the right dot. + +Integer tokens cannot be involved in this syntax, because they +form floating-point constants when juxtaposed with a dot. +Such ambiguous uses of floating-point tokens are diagnosed as syntax errors: + +.cblk + (a.4) ;; error: cramped floating-point literal + (a .4) ;; good: a followed by 0.4 +.cble + + .NP* Quote and Quasiquote .meIP >> ' expr |