dsl.stxt

Here's as toy domain-specific language:

"""
Language specifications

functions
    add     : sum all arguments
    sub     : subtract tail from head
types
    int
    float
arguments
    out     : stdin to use previous output as input
            : stdout to print
"""

program = """
Module add 1 2 3 type=float out=stdin
Module sub stdin 1 2 type=int out=stdout
"""

Implement this in as few lines of Python as possible.
> f={'add':lambda *a:sum(a),'sub':lambda a,*b:a-sum(b)}; prev=None
> for l in program.splitlines():
>     if not l.strip(): continue
>     t=l.split(); kv=dict(x.split('=') for x in t if '=' in x); typ={'int':int,'float':float}[kv.get('type','int')]
>     prev=f[t[1]](*[typ(prev) if x=='stdin' else typ(x) for x in t[2:] if '=' not in x])
>     if kv.get('out')=='stdout': print(prev)