parson/eg_calc_compile.py at master · darius/parson · GitHub

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"""
After http://www.vpri.org/pdf/rn2010001_programm.pdf
"""

from parson import Grammar

def assign(v, exp):  return exp(0) + ['sw r0, ' + v]

def ld_const(value): return lambda s: ['lc r%d, %d' % (s, value)]
def ld_var(name):    return lambda s: ['lw r%d, %s' % (s, name)]

def add(exp1, exp2): return lambda s: (exp1(s) + exp2(s+1)
                                       + ['add r%d, r%d, r%d' % (s, s+1, s)])
def mul(exp1, exp2): return lambda s: (exp1(s) + exp2(s+1)
                                       + ['mul r%d, r%d, r%d' % (s, s+1, s)])

g = Grammar(r"""  stmt :end.

stmt  :  ident ':=' exp0   :assign.

exp0  :  exp1 ('+' exp1    :add)*.
exp1  :  exp2 ('*' exp2    :mul)*.

exp2  :  '(' exp0 ')'
      |  /(\d+)/ :int      :ld_const
      |  ident             :ld_var.

ident :  /([A-Za-z]+)/.

FNORD~:  /\s*/.

""")(**globals()).expecting_one_result()

## for line in g('v := 42 * (5+3) + 2*2'): print line
#. lc r0, 42
#. lc r1, 5
#. lc r2, 3
#. add r1, r2, r1
#. mul r0, r1, r0
#. lc r1, 2
#. lc r2, 2
#. mul r1, r2, r1
#. add r0, r1, r0
#. sw r0, v