[Omake] String manipulation

[Jason Hickey]

Oops, the subst function I sent earlier has a mistake--the  
replacement wasn't being evaluated.  Here is an updated version.

Input string  is: ABCx123x456xDEFx555x666x
Output string is: ABCy456y123yDEFy666y555y

Jason

#
# Replace all occurrences of $(from) with $(to)
# in the string $s, returning the result as a string.
# The $(to) should be a function of one argument.
#
# In $(to), $0 stands for the entire match, and $i stands
# for the i'th match part\(...\).
#
subst(from, to, s) =
    # Create a channel from a string
    inx = $(open-in-string $s)

    # Perform the substitution collecting results
    result[] =
    lex-search($(inx))
    case $(from)
        # Evaluate the replacement in this context
        result[] += $(string $(to))
        export
    default
        result[] += $0
        export

    # Remember to close the input
    close($(inx))

    # Flatten into a normal string
    concat($(EMPTY), $(result))

# Example
in = ABCx123x456xDEFx555x666x
out = $(subst $'x\([0-9]+\)x\([0-9]+\)x', $(fun y$2y$1y), $(in))

println($"Input string  is: $(in)")
println($"Output string is: $(out)")

--
Jason Hickey                  http://www.cs.caltech.edu/~jyh
Caltech Computer Science      Tel: 626-395-6568 FAX: 626-792-4257