ModaLogic Functional/Technical Design Documentation¶
Expression Rewriter Module¶
It all starts with the ExpressionRewriter. This component will take a possibly in ascii writtern argument and converts it into a consistent format based on on UTF8 "symbols". This is to support the parser by providing a consistent foundation to lex and parse.
The ExpressionRewriter handles the conversion of the expressions of a modal logic argument and converts them into a consistent format that the parser can handle. The parser expects all operators to be single symbols --not ascii representations that use possilbe multiple characters for a single operator.
For instance a user might want to enter the iff operator with an ascii input string which would look like '<-->' but the parser want a single logic symbol like: '↔'. The ExpressionRewriter will handle such conversions.
ExpressionRewriter
¶
toSymbols(str)
classmethod
¶
This function takes an ascii string representing the expression and replaces the ascii-symbols into UTF symbols.
1 | |
Source code in modalogic\textio\ascii_io.py
@classmethod
def toSymbols(cls, str):
""" This function takes an ascii string representing the expression
and replaces the ascii-symbols into UTF symbols.
str = re.sub(r"^\((.*)\)$", r"\g<1>", str)
"""
str = str.replace('&', '∧')
str = str.replace('^', '∧')
str = str.replace('<->', '↔')
str = str.replace('->', '→')
str = str.replace('~', '¬')
str = str.replace(' v ', ' ∨ ') # 'v' letter => or symbol
str = str.replace('[]', '□')
str = str.replace('<>', '◇')
str = re.sub(r"\(A([s-z])\)", r"∀\g<1>", str) # (Ax) => ∀x
str = re.sub(r"\(E([s-z])\)", r"∃\g<1>", str) # (Ex) => ∃x
str = re.sub(r"\forall[\{ ]?\}?/g", '∀', str)
str =re.sub(r"\\[Bb]ox[\{]?[\} ]?", r"□", str)
str = re.sub(r"\\[Dd]iamond[\{ ]?\}?", '◇', str)
str = re.sub(r"\\exists[\{ ]?\}?", '∃', str)
str = re.sub(r"(\\neg|\\lnot)[\{ ]?\}?", '¬', str)
str = re.sub(r"(\\vee|\\lor)[\{ ]?\}?", '∨', str)
str = re.sub(r"(\\wedge|\\land)[\{ ]?\}?", '∧', str)
str = re.sub(r"(\\to|\\rightarrow)[\{ ]?\}?", '→', str)
str = re.sub(r"\\leftrightarrow[\{ ]?\}?", '↔', str)
str = re.sub(r"(?:^|\W)\(([s-z])\)", r"∀\g<1>", str)
# str =re.sub(r"(?:^|\W)\(([s-z])\)", '∀$1', str) # (x) => ∀x, but not f(x) => f∀x
return str