PM Programming Language

One of the features designed to make PM convenient for numerical computation is its notation for subexpressions. Any PM expression may be followed by a list of subexpressions introduced by the where keyword. Hdist = 1 –sqrt( 2*s1*s2/ss) * exp ( - (m1-m2)**2 / ss / 4 ) where ss = s1**2 + S2**2 Subexpressions may not refer to each other in the same list, but you can add any number of lists after a given expression: Hdist = 1 –sqrt( 2*s1*s2/ss) * exp ( - (m1-m2)**2 / ss / 4 ) where ss = s1**2 + S2**2 where m1=mean(x), m2=mean(y), s1=stddev(x), s2=stddev(y) In some contexts where clauses apply to a list of expressions, for example: for i in a[r], j in b[r], k in c[r] where r=grid(xlo..xhi,ylo..yhi,zlo..zhi) do … endfor A   PM expression may also be combined with an assertion by placing a check clause between the expression and any following subexpressions: x=solve(f,y) check f(x)-y < tolerance The check clau...

PM adopts a clean approach to statement separation. PM statements are formally separated by semicolons. However, these may be omitted if the next statement starts on a new line. This is the only syntactic role for line breaks – statements and expressions may sprawl across as many lines as you wish. For die-hard C/C++/Java programmers, it is also possible to add a semicolon at the end of a statement list. a=1; b=2; c=1 x = -b + sqrt( b**2 - 4 * a * c) / 2*a print("x="//x) Semicolons are also used in constructors for two-dimensional data structures: arrays and matrices.   Line breaks can be substituted for semicolons here too, enabling you to write something like: id_matrix = ( 1,0,0 0,1,0 0,0,1 )