SRFI-105 "Curly Infix" for Racket🔗ℹ

1.1 Strict mode: using the reader as the original SRFI 105🔗ℹ

Between BEGIN-STRICT-SRFI-105-REGION and END-STRICT-SRFI-105-REGION the reader follows SRFI 105, as the original reader: {a} is a, {a b} is (a b), {a op b op c} with a single operator is (op a b c) (also with if), the () are not infix, and the other expressions are ($nfx$ …). As in SRFI 105, the neoteric expressions f(x), f{x} and x[i] are recognized only inside curly brackets, in both modes: outside, f(x) is read as the two data f and (x).

The main differences with the rules of Scheme+:

Racket defines neither $nfx$ (used for the expressions that are not simple infix) nor $bracket-apply$ (used for x[i]): SRFI 105 leaves them to the programmer. Define them yourself, or take them from Scheme+, where $nfx$ evaluates the expression with the precedence of the operators. A whole file in strict mode, as with the original reader:

#lang reader SRFI-105

BEGIN-STRICT-SRFI-105-REGION

(module m racket

(require (only-in Scheme+ $nfx$ $bracket-apply$))

(define (f x) {x * 2})

(define v #(10 20 30))

(display (list {2 + 3 * 4} {f(5) + v[1] * 2} '{a + b * c}))

(newline))

displays (14 50 ($nfx$ a + b * c)).

At the REPL, type the pragma alone (or alone in curly brackets): the mode changes for the rest of the session.

1.2 Type annotation: ANNOTATION-ON and ANNOTATION-OFF🔗ℹ

The pragmas ANNOTATION-ON and ANNOTATION-OFF turn on or off, by region, the type annotation and inference pass of Scheme+ (see the section Type annotation and inference of the Scheme+ documentation): a pragma acts on the elements that follow it in the same list and on all that is nested in them, until the other pragma or the end of the list. The pass is off at the beginning of each file: a pragma acts only on the file where it is written, not on the modules this file requires. It can be written inside the module form or at the top level of the file (before the module form, it acts on the whole module).

At the REPL, type the pragma alone: it turns the annotation on or off for the rest of the session, the expressions typed between ANNOTATION-ON and ANNOTATION-OFF are a region. The REPL starts in the state left by the file it was started from (REPL-Scheme-PLUS.rkt of Scheme+ has ANNOTATION-ON), and ANNOTATION-ON also works in a REPL started without a file: it then creates the tables of the annotation, the tables of a file already read are kept.

1.3 Quoted lists: CARE-OF-QUOTES-ON and CARE-OF-QUOTES-OFF🔗ℹ

The pragmas CARE-OF-QUOTES-ON and CARE-OF-QUOTES-OFF act by region too, on the quoted lists (see the section Pragmas of the Scheme+ documentation): with CARE-OF-QUOTES-ON, the state at the beginning of each file, a quoted list is data and a quoted {} is converted at its top level only; CARE-OF-QUOTES-OFF opens a region for the symbolic computation, where the quoted and quasiquoted lists are infix expressions at all levels ('(x + y * z) is '(+ x (* y z))).