2025/12/11

Alternative external formats for arrays and complex numbers

Gauche now recognizes a few different external format for arrays and complex numbers. For writing, it can be selected by <write-controls> object, or print-mode in REPL.

Array literals

Gauche has been supporting srfi:25 arrays, but it does not define external representations. Gauche uses srfi:10 #, mechanism to allow to write arrays that can be read back, but it is not very user-frendly.

gosh$ (tabulate-array (shape 0 4 0 4) *)
#,(<array> (0 4 0 4) 0 0 0 0 0 1 2 3 0 2 4 6 0 3 6 9)

Now we have this:

gosh$ (tabulate-array (shape 0 4 0 4) *)
#2a((0 0 0 0)
    (0 1 2 3)
    (0 2 4 6)
    (0 3 6 9))

The #2a(...) notation is defined in srfi:163 Enhanced Array Literals, and in its simplest form, it is also compatible to Common Lisp's array literals. From 0.9.16, it is the default output format of the array.

You can also make Gauche reports the lengthes of each dimension:

gosh$ ,pm array dimensions
Current print mode:
       length :  50         pretty :  #t     bytestring :  #f
        level :  10           base :  10          array : dimensions
        width :  80   radix-prefix :  #f        complex : rectangular
string-length : 256  exact-decimal :  #f
gosh$ (tabulate-array (shape 0 4 0 4) *)
#2a:4:4((0 0 0 0)
        (0 1 2 3)
        (0 2 4 6)
        (0 3 6 9))

The reader recognizes all of those formats.

Complex literals

There was an asymmetry in input/output of complex literals. For reading, both the rectangular notation 1.4142135623730951+1.4142135623730951i and the polar notation 2@0.7853981633974483 are recognized, but for printing, it is alyways in the rectangular notation. Now you can choose the output format.

Gauche also extended the polar notation by adding suffix pi, e.g. 2@0.25pi to specify the phase by the multiple of pi.

The following session shows how a complex number is printed with different print-mode:

gosh> (expt -16 1/4)
1.4142135623730951+1.4142135623730951i
gosh> ,pm polar
Current print mode:
       length :  50           base :  10  exact-decimal :  #f
        level :  10   radix-prefix :  #f          array : compact
       pretty :  #t  string-length : 256        complex : rectangular
        width :  79     bytestring :  #f
gosh> (expt -16 1/4)
2.0@0.7853981633974483
gosh> ,pm complex polar-pi
Current print mode:
       length :  50           base :  10  exact-decimal :  #f
        level :  10   radix-prefix :  #f          array : compact
       pretty :  #t  string-length : 256        complex : polar-pi
        width :  79     bytestring :  #f
gosh> (expt -16 1/4)
2.0@0.25pi

Furthermore, Gauche also supports Common-Lisp style complex notation, #c(...). This is particulary useful to exchange data between Gauche and CL programs.

gosh> ,pm complex vector
Current print mode:
       length :  50           base :  10  exact-decimal :  #f
        level :  10   radix-prefix :  #f          array : compact
       pretty :  #t  string-length : 256        complex : vector
        width :  79     bytestring :  #f
gosh> (expt -16 1/4)
#c(1.4142135623730951 1.4142135623730951)

The reader can read all the complex formats.

Tags: 0.9.16, REPL, printer, array, complex