ever-to-excel's Introduction

ever-to-excel

Compile programs to spreadsheets.

Example

Input

The input language is called Ever. It's a restricted variant of Scheme.

(define (fac acc n)
  (if-zero
    n
    acc
    (fac (* n acc) (- n 1))))

(define (main)
  (display
    (fac 1 6)))

Bytecode

Ever compiles to instructions for a stack VM.

; -------[ main ] -------------
OP 0 (XStr "ret")
OP 0 (XInt 1)
OP 0 (XInt 6)
LOAD (Addr 3)
PUSHL (PC 8)
LOAD (Addr 2)
STORE (Addr 3)
JMP (PC 13)
LABEL (PC 8)
STORE (Addr 3)
POP 2
PRINT
HALT
; -------[ fac ] --------------
LABEL (PC 13)
OP 0 (XLoc 2)
JZ (PC 22)
OP 0 (XOp "*" (XLoc 2) (XLoc 3))
OP 0 (XOp "-" (XLoc 2) (XInt 1))
LSTORE 2
LSTORE 3
JMP (PC 13)
JMP (PC 24)
LABEL (PC 22)
OP 0 (XLoc 3)
LABEL (PC 24)
LSTORE 4
RET

Output

Some details

The input language, Ever, looks like Scheme but it's restricted even more than C.

You cannot have local variables (there's no let).
You cannot access the parent scope.
There is no heap, no dynamic allocation, no closures.

All of the above can be addressed; it just needs more work. :)

However:

You can have (mutual) recursion.
Tail recursion is supported (at the moment only for tail calls with the same number of arguments).
There are some spreadsheet-specific optimisations, e.g. compiling expressions directly to spreadsheet expressions rather than into multiple instructions, whenever possible.

More details:

Every row in the spreadsheet is the same. (Except for the initial row, which does not contain any formulas.)
We could make every cell the same but we use the static knowledge of the column number to make some optimisations.
The compiler runs the program in the interpreter first to determine the minimal width and height of the spreadsheet. This is not cheating; it's fine to generate more cells than necessary.

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