autoload(Symbol,String) -- arrange for a function to be loaded automatically

Synopsis

Usage:
autoload(f,x)
Function: autoload
Inputs:
- f, a symbol
- x, a string
Consequences:
- arranges for a function named f to be automatically loaded from the file x the first time it is used. This is accomplished by creating a suitable function that will load the file and assigning the function to f.

Description

i1 : fn = temporaryFileName()

o1 = /tmp/M2-22111-1

i2 : fn << "f = x -> x+1\n" << close

o2 = /tmp/M2-22111-1

o2 : File

i3 : autoload(f,fn)

i4 : code f

o4 = -- ../m2/autoload.m2:5-11
          sym <- f := x -> (
               load filename;
               if f === value sym 
               then error("symbol '", toString sym, "' didn't acquire a new value in file '", filename, "'");
               (value sym) x
               );
          )
     | symbol     class              value                                     location of symbol
     | ------     -----              -----                                     ------------------         
     | sym      : Symbol          -- f                                         ../m2/autoload.m2:3:28-3:28
     | filename : String          -- "/tmp/M2-22111-1"                         ../m2/autoload.m2:3:32-3:32
     | f        : FunctionClosure -- {*Function[../m2/autoload.m2:5:19-9:22]*} ../m2/autoload.m2:5:12-5:12

i5 : f 4
--warning: f redefined

o5 = 5

i6 : removeFile fn