write an interpreter understanding nested commands

Question

Please write an interpreter that understands the commands input and output. Output shall do the same as echo, print or cout in real-world languages. Input shall do the same as read, input or cin: it shall return the string entered by the user. Your interpreter shall be able to execute

output("Hello "+input("What is your name ? "))

Execution will then look like:

What is your name ? Thorsten
Hello Thorsten

Note that in order to execute the outer command (output) the execution of the nested (inner) command (input) is needed. input returns Thorsten in this case and output prints it. Your take how you deal with parentheses and operators like +. Please make your interpreter extendable so do not scan for "input" and "output" as keywords.

Answer 1

Python 3 (43 bytes)

I don't think it can be shorter than this. You may consider it to be cheating, but there is nothing in rules against this (at least, there wasn't when I wrote that).

from sys import*
output=print
eval(argv[1])

Sample output:

$ python3 interpreter.py 'output("Hello "+input("What is your name ? "))'
What is your name ? Thorsten
Hello Thorsten

Python 3 REPL (12 bytes)

Alternatively, if you are going to consider squeamish ossifrage's solution to be legit, this is a shorter solution having just 12 bytes. After you run a single line of code, the Python REPL turns into Your Language REPL.

output=print

Sample output:

$ python3
Python 3.3.2 (default, Nov  7 2013, 10:01:05) 
[GCC 4.8.1 20130814 (Red Hat 4.8.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> output=print
>>> output("Hello "+input("What is your name ? "))
What is your name ? Thorsten
Hello Thorsten
>>>

Answer 2

Ruby

Code golf was not specified, so I didn't golf it.

$funcs = {
    input: ->arg{ print arg; gets.chomp },
    output: ->arg{ puts arg; arg }
}

def pass code
    changed = false
    code.gsub!(/([a-z]+)\("([^"]*)"\)/) { changed = true; "\"#{$funcs[$1.to_sym][$2]}\"" }
    code.gsub!(/"([^"]*)"\+"([^"]*)"/) { changed = true; "\"#{$1 + $2}\"" }
    changed
end

code = 'output("Hi "+input("Enter your name: "))'
nil while pass code

pass is a function that takes the code and scans for either a function call or a string concatenation. If it finds either of those, it returns true, otherwise nothing was changed so it returns false to signify that you should stop passing.

Answer 3

Javascript console: 25 bytes

This is too easy.

output=alert;input=prompt